WBBSE Solutions For Class 6 Maths Chapter 19 Measurement Of Time

Class 6 Math Solutions WBBSE Chapter 19 Measurement Of Time Exercise 19

Question 1. Given below is the time chart of Priya on a holiday. Let’s try to get few information.
Solution:

On that day, Priya woke up: at 6.00 a.m

Priya studied at: 9.00 a.m

Priya gossips with friends at: 11.00 a.m

She had lunch at: 1.00 a.m

After lunch at: 4.00 p.m

On that day Priya went to bed: at 10.00 p.m

Question 2. Today I left my house at 10:20 a.m. for school. Returned home at 4:45 p.m. Let’s calculate how long I was out of home.
Solution:

I was out of home = 4:45 p.m – 10:20 am = 6 hrs 25 min

Question 3. Yesterday Deba went to bed at 10: 25 p.m. But today he woke up at 6:10 a.m. Let’s find out how long he slept.
Solution:

Deba slept = 6:10 a.m – 10: 25 p.m = 7 hrs 45 mins

Read and Learn More WBBSE Solutions For Class 6 Maths

Question 4. Today I am going to Puri with my family. The train will leave from Howrah station at 22:35 hours, we will reach Howrah station at 20:44 hrs. Let’s calculate how long we have to wait at the station.
Solution:

We have to wait at the station = 22:35 hours – 20:44 hours

= 1 hour 51 mins Hrs min

⇒ \(\begin{array}{lc}
\text { Hrs } & \text { min } \\
22 & 35 \\
20 & 44 \\
\hline 1 & 51 \\
\hline
\end{array}\)

Class 6 Math Solutions WBBSE

Question 5. Today I have a history examination. Exam started at 11: 30 a.m. The teacher’s digital wristwatch is showing 13:15. Let me find out how long I had already written the examination. If the exam is to end at 2:30 p.m., how long shall I be able to write the examination, when the exam will be over, let me find out what will the digital watch of the teacher read.
Solution:

I had already written the examination = 13:15 – 11:30 am = 1 hr 45 min.

I shalf be able to write the examination = 2:30 p.m. -13:15 = 1 hr 15 min.

The time of digital watch of the teacher = 13:15 + 1 hr 15 min = 14:30.

Question 6. To reach father’s office from home, it takes 2 hrs 27 min but while returning home, it takes 2 hrs 51 min. Let me find out how long it takes in total to go to my father’s office and back.
Solution:

The time to go to father’s office and back

= 2 hrs 27 mins + 2 hrs 57 mins

= 5 hrs 24 mins.

⇒ \(\begin{array}{lll}
\text { Hrs } & \min & \\
2 & 27 & \\
2 & 57 & \\
5 & 24 &
\end{array}\)

⇒ \(\begin{array}{rcc}
7 . \mathrm{hr} & \min & \mathrm{sec} \\
8 & 32 & 41 \\
+18 & 42 & 25 \\
& 74 & 66 \\
\hline \mathrm{hrs} & \min & \mathrm{sec} \\
\hline
\end{array}\)

Solution:

1. \(\begin{array}{rrr}
\mathrm{hr} & \mathrm{min} & \mathrm{sec} \\
8 & 32 & 41 \\
+18& 42 & 25 \\
26 & 74 & 66 \\
\hline 27 \mathrm{hrs} & 15 \mathrm{~min} & 6 \mathrm{sec} \\
\hline
\end{array}\)

2. \(\begin{array}{ccc}
\text { 2 hr } & \text { min } & \text { sec } \\
\text { (8) } & 60+11 & 60+37 \\
9 & 12 & 37 \\
-3 & 38 & 41 \\
\hline 5 \mathrm{hr} & 33 \mathrm{~min} & 56 \mathrm{sec} \\
\hline
\end{array}\)

Class 6 Math Solutions WBBSE

Question 8. Let’s add and subtract

1. (4 hr 33 min 20 sec) + (9 hr 52 min 25 sec)
Solution:

⇒ \(\begin{array}{ccc}
\text { Hrs } & \text { Mins } & \text { Sec } \\
4 & 33 & 20 \\
+9 & 52 & 25 \\
13 & 85 & 45 \\
\hline=14 \mathrm{Hrs} & 25 \mathrm{~min} & 45 \mathrm{sec} . \\
\hline
\end{array}\)

2. (6 hr 42 min 2 sec) – (2 hr 55 min 42 sec)
Solution:

⇒ \(\begin{array}{ccc}
\text { Hrs } & \text { Min } & \text { Sec } \\
5 & 60+41 & 60+2 \\
6 & 42 & 2 \\
-2 & 55 & 42 \\
\hline 3 & 46 & 20
\end{array}\)

= 3 hrs 46 min 20 Sec

3. (18 hr 19 min 15 sec) + (9 hr 55 min 48 sec)
Solution:

⇒ \(\begin{array}{rcc}
\text { Hrs } & \text { Min } & \text { Sec } \\
18 & 19 & 15 \\
9 & 55 & 48 \\
\hline 27 & 74 & 63 \\
\hline
\end{array}\)

= 28 hrs 15 min 3 sec

4. (23 hr 7 min) – (19 hr 29 min 18 sec)
Solution:

⇒ \(\begin{array}{ccc}
\text { Hrs } & \min& \text { Sec } \\
22 & 60+6 & 60+0 \\
23 & 7 & 00 \\
9 & 55 & 48 \\
\hline 13 & 11 & 12 \\
\hline
\end{array}\)

= 13 hrs 11 min 12 Sec.

Class 6 WBBSE Math Solutions Chapter 19 Measurement Of Time Exercise 19.1

Question 1. Debubabu built a new house. He will paint the two windows of his house. Each window has two panes. If he takes 2 hr 15 min to paint 1 window pane, let’s find how long he will take to colour 2 windows.
Solution:

Time required to paint 1 window pane = 2 hrs 15 m

∴ Time required to paint 2 window panes = 2 hr 15 min x 2 = 4 hrs 30 min

Question 2. In 11 hrs 36 min, Phani Da can make 4 exactly similar clay statues. Let’s find out how long he will take to make one such statue. He takes equal time to make each statue.
Solution:

Time required to make 4 clay statues = 11 hrs 36 min

∴ Time required to make 1 clay statue = 11 hr 36 min ± 4

WBBSE Solutions For Class 6 Maths Chapter 19 Measurement Of Time 11 hr 36 min divisible by 4

= 2 hrs 54 mins.

Question 3.

1. 3 hrs 26 min x 4 = How many hours and minutes?
Solution:

3 hrs 26 min x 4

= 12 hr 104 min = 13 hrs 44 min

2. 7 hrs 13 min x 12 = How many hours and minutes?
Solution:

7 hrs 13 min x 12

= 84 hrs 156 min = 86 hr. 36 min

Class 6 WBBSE Math Solutions

3. 3 hrs 27 min ÷ 9 = How many minutes and seconds?
Solution:

WBBSE Solutions For Class 6 Maths Chapter 19 Measurement Of Time 3 hr 27 min divisible by 9

4. 15 hrs ÷ 12 = How many hrs and mins?
Solution:

WBBSE Solutions For Class 6 Maths Chapter 19 Measurement Of Time 15 hrs 12 min divisible by 12

5. 6 hrs 18 sec ÷ 9 = How many min, sec?
Solution:

WBBSE Solutions For Class 6 Maths Chapter 19 Measurement Of Time 6 hrd 18 sec divisible by 9

6. 5 hrs10 min 4 sec ÷ 4 = How many hours, min, sec?
Solution:

WBBSE Solutions For Class 6 Maths Chapter 19 Measurement Of Time 5 hrs 10 min 4 sec divisble by 4

Class 6 WBBSE Math Solutions

7. 2 hrs 32 min 41 sec÷ 3 = How many hours, min, secs?
Solution:

2 hr 32 min 4 sec x 3

2 hr 32 min 4 sec x 3

6 hr 96 min 12 sec

= 7 hr 36 min 12 sec

Class 6 Maths Solutions WBBSE Chapter 19 Measurement Of Time Exercise 19.1

Question 1. 1st February of 2010 was Monday. Let’s calculate 1st March 2010 and 1st April 2010 will be which days.
Solution:

1 st February 2010 was monday and February has 28 days.

∴ 1st March 2010 was Monday and March has 31 days.

∴ 3 days after Monday is Thursday.

∴ 1st April 2010 is Thursday.

Question 2. 01/02/2012 was Wednesday, then let’s calculate which days were the following dates: 01/03/2012, 01/04/2012, 01/05/2015,04/06/2012
Solution:

1st February of 2012 was Wednesday and February 2012 had 29 days.

∴ 1 day after Wednesday is Thursday.

∴ . 1st March 2012 was Thursday.

March has 31 days.

3 days after Thursday is Sunday.

∴ 1st April 2012 was Sunday.

April has 30 days.

2 days after Sunday is Tuesday.

∴ 1st May 2012 was Tuesday.

May has 31 days, 6 days after Tuesday is Monday.

4th June 2012 is Monday.

Class 6 Maths Solutions WBBSE

Question 3. 1st January of 1996 was Sunday. Let us calulate which day 1st January of 1997 will be.
Solution:

1st January 1996 was Monday.

Since 1996 was a leap year so 1996 had 366 days.

2 days after Monday is Wednesday.

∴ 1st January 1997 was Wednesday.

Question 4. 1st March of 2004 was Monday, which day will be 1st April of 2005.
Solution:

1st March 2004 was Monday 2005 year had 365 days.

1 day after Monday is Tuesday.

1st March 2005 was Tuesday

1st March 2005 had 31 days.

3days after Tuesday is Friday.

∴ 1st April 2005 was Friday.

Question 5. 1st June of 2008 was Tuesday. Let’s calculate which day was 1st June of 2006.
Solution:

1st June 2008 was Sunday. 2008 was a leap year.

So, 2008 had 366 days.

2006 and 2007 had 365 days.

4days before Sunday is Thursday.

1st June 2006 was Thursday.

Class 6 Maths Solutions WBBSE

Question 6. Independence day of 2013 is Thursday, let’s find which day will be Independence day of 2016.
Solution:

Independence day of 2013, 15th August 2013 was Thursday.

2013 had 365 days and 2016 is a leap year.

So 2016 has 366 days.

4 days after Thursday is Monday.

∴  Independence day of 2016 will be Monday.

Question 7. From the calendar of 2013 let us write which day of the week are the following and without looking into calender, let’s find which days of the week these days were in the year 2011 — Children’s day, Teachers’ day, Gandhi birthday, Republic day, Netaji Jayanti, World environment day (5th of June).
Solution:

1. Children’s Day (14th November)

14th November 2013 was Thursday.

2014 had 365 days and 2012 had 366 days.

3 days before Thursday is Monday.

2. Teachers’ day (5th September)

5th September of 2013 was Thursday.

2011 had 365 days and 2012 had 366 days.

3 days before Thursday is Monday.

∴ Teachers’ day – 5th September 2011 was Monday.

WBBSE Math Solutions Class 6

3. Gandhi birthday – 2nd October.

2nd October 2013 was Wednesday.

2011 had 365 days and 2012 had 366 days.

3 days before Wednesday Sunday.

∴ Gandhi birthday (2nd October) 2011 was Sunday.

4. Republic day (26th January)

26th January of 2013 was Saturday.

2011 had 365 days and 2012 had 366 days.

3 days before Saturday is Wednesday.

∴ Republic day (26th January, 2011) was Wednesday.

5. Netaji Jayanti (23rd January)

23rd January 2013 was Wednesday.

2011 had 365 days and 2012 had 366 days.

3 days before Wednesday is Sunday.

∴ Netaji Jayanti (23rd January) 2011 was Sunday.

6. World Environment Day (5th June)

5th June 2013 was Wednesday.

2011 had 365 days and 2012 had 366 days.

3 days before Wednesday is Sunday.

World Environment Day 5th June, 2011 was Sunday.

WBBSE Math Solutions Class 6

Question 8.

  1. Let’s write the leap years between 1895 to 1915.
  2. Let’s write the leap years between 2010 to 2030.

Solution:

  1. Leap years between 1895 to 1915 = 1896; 1900; 1904,1908, and 1912.
  2. Leap years between 2010 to 2030 = 2012, 2016, 2020, 2024, and 2028.

Question 9. I stayed for 4 years in a house at College Ghat Road, from 2010 to 2013. Let’s calculate for how many days I stayed in that house.
Solution:

In 2010 – Number of days = 365 In 2011 — Number of days = 365

In 2012 — Number of days = 366 In 2013 — Number of days = 365 Total days in 4 years = 365 + 365 = 366 + 365 = 1461

Question 10. My birthday is on 15th December. In 2013, my birthday was on Sunday. Which day of the week will my birthday be in the years 2014, 2015 and 2016?
Solution:

My birthday is on 15th December 2013, which was Sunday. In 2014 had 365 days

1 day after Sunday is Monday.

∴ 15th December 2014 was Monday.

In 2015 had 365 days.

∴ 1 days after Monday is Tuesday.

∴ 15th December, 2015 is Tuesday.

2016 is of 366 days.

∴ 2 days after Tuesday is Thursday.

∴ 15th December 2016 will be Thursday.

Question 11. After independence, how many leap years have passed till 2014?
Solution:

Independence day was 15th August 1947.

The leap years that have passed till 2014 are 1948,1952,1956,1960,1964,1968 1972,1976,1980,1984,1988,1992 1996, 2000, 2004,2008 and 2012.

WBBSE Class 6 Maths Solutions Chapter 19 Measurement Of Time Exercise 19.2

Question 1. My date of birth is 19 -11 -1975, i.e., 19th November 1975. Let us find my
Solution:

⇒ \(\begin{array}{lll}
\text { Years } & \text { Months } & \text { Days } \\
& 12+9 & 30+10 \\
2010 & 10 & 10 \\
-1975 & 11 & 19 \\
\hline 24 & 10 & 21 \\
\hline
\end{array}\)

= 24 years 10 months 21 days.

Question 2. The construction of our main road began in summer on 6/6/2010. It took 1 yr 3 months 18 days to finish the work. Let’s calculate to find on which date the road construction work was completed.
Solution:

⇒ \(\begin{array}{ccc}
\text { Years } & \text { Months } & \text { Days } \\
2010 & 06 & 06 \\
+\quad 1 & 03 & 18 \\
\hline 2011 & 09 & 24 \\
\hline
\end{array}\)

The date of road construction work was completed on 24/09/ 2011.

Question 3. My present age is 11 yrs 7 months 10 days. Let me calculate after how many years I shall be eligible to cast my vote.
Solution:

⇒ \(\begin{array}{cll}
\text { Years } & \text { Months } & \text { Days } \\
17 & 12+0 & 30 \\
(-) 11 & 07 & 10 \\
\hline 6 & 08 & 20 \\
\hline
\end{array}\)

= 6 yrs 04 months 20 days.

WBBSE Class 6 Maths Solutions

Question 4. The age of my father is 52 years 8 months 20 days. My uncle is 3 years 10 months 26 days older than my father. Let me find the age of my uncle.
Solution:

⇒ \(\begin{array}{ccl}
\text { Years } & \text { Months } & \text { Days } \\
52 & 8 & 20 \\
+3 & 10 & 26 \\
\hline 56 & 7 & 16 \\
\hline
\end{array}\)

= Age of my uncle = 56 years 7 months 16 days.

Question 5. Let us find values

1. \(\begin{array}{rcc}
\text { Year } & \text { Months } & \text { Days } \\
9 & 10 & 27 \\
+\quad 5 & 8 & 21 \\
\hline 14 & 18 & 48 \\
\hline
\end{array}\)

Solution: 15 years 7 months 18 days.

2. \(\begin{array}{ccc}
\text { Year } & \text { Month } & \text { Days } \\
29 & 11 & 19 \\
5 & 9 & 25 \\
+6 & 3 & 13 \\
\hline 40 & 23 & 57 \\
\hline
\end{array}\)

Solution: 42 years 0 months 27 days

3. \(\begin{array}{ccl}
\text { Year } & \text { Month } & \text { Days } \\
& 12+3 & 30 \\
11 & 3 & \mathrm{x} \\
-6 & 10 & 28 \\
\hline 5 & 5 & 02 \\
\hline
\end{array}\)

Solution: 5 years 5 months 2 days.

4. \(\begin{array}{|c|c|c|}
\hline \text { Year } & \begin{array}{c}
\text { Month } \\
12+6
\end{array} & \begin{array}{l}
\text { Days } \\
30+19
\end{array} \\
\hline 11 & 6 & 19 \\
\hline-6 & 10 & 21 \\
\hline 5 & 8 & 28 \\
\hline
\end{array}\)

Solution: 5 years 8 months 28 days.

Class 6 Math WBBSE Solutions

Question 6. (1) 8 yrs 8 months 28 days + 11 yrs 8 months 18 days = How many yr, months and days?
Solution:

⇒ \(\begin{array}{rcl}
\text { Years } & \text { Months } & \text { Days } \\
8 & 8 & 28 \\
+11 & 8 & 18 \\
\hline 19 & 16 & 46 \\
\hline
\end{array}\)

= 20 yrs 5 months 16 days.

2. 20 yrs 11 months and days? -10 yrs 8 months 23 days = How many yr, month
Solution:

⇒\(\begin{array}{ccc}
\text { Years } & \text { Months } & \begin{array}{c}
\text { days } \\
30+0
\end{array} \\
20 & 11 & 0 \\
10 & 89 & 23 . \\
\hline 10 & 2 & 7 \\
\hline
\end{array}\)

= 10 years 2 months 7 days

3. 8 yrs 7 months 21 days x 9 = How many yr, month and days?
Solution:

= 77 yrs.9 months 9 days.

Question 7. My age is □ yrs □ months □ days. The age of my friend is □ yrs □ months □ days. What is the sum of our age and who is older than the two and by how much? Let us find out.
Solution:

My age is 15 years 11 months 26 days. The age of my friend is 14 yrs 9 months 20 days.

⇒ \(\text { Sum }=\begin{array}{ccc}
\text { Year } & \text { Month } & \text { Days } \\
15 & 11 & 26 . \\
14 & 9 & 20 \\
\hline 29 & 20 & 46 \\
\hline
\end{array}\)

= 30 yrs 9 months 16 days.

I am older than my friends.

Difference

⇒ \(\begin{array}{lll}
\text { Years } & \text { Month } & \text { Days } \\
15 & 11 & 26 \\
14 & 9 & 20 \\
\hline 1 & 2 & 6 \\
\hline
\end{array}\)

= 1 yr 2 months 6 days.

Class 6 Math WBBSE Solutions

Question 8. My date of birth is □. Today my age is □ yrs □ months □ days.
Solution:

My date of birth is 04.10-2001

Today my age is — (19-11 -2014)

⇒ \(\begin{array}{rll}
\text { Year } & \text { Month } & \text { Days } \\
2014 & 11 & 19 \\
-2001 & 10 & 04 \\
\hline 13 & 1 & 15 \\
\hline
\end{array}\)

Today my age is 13yrs 1month 15days

WBBSE Solutions For Class 6 Maths Chapter 21 Fundamental Concept Of Ratio And Proportion

Class 6 Math Solutions WBBSE Chapter 21 Fundamental Concept Of Ratio And Proportion

We take lengths of our pen caps and lengths of pens without cap and try to take their ratio and write them in a table like below.

WBBSE Solutions For Class 6 Maths Chapter 21 Fundamental Concept Of Ratio And Proportion Length Of Our Pen Caps And Pens Without Cap

Let us see the picture count the number ratio in its lowest form and write the ratio.

WBBSE Solutions For Class 6 Maths Chapter 21 Fundamental Concept Of Ratio And Proportion Count The Number Ration In Its Lowest Form

Class 6 WBBSE Math Solutions Chapter 21 Fundamental Concept Of Ratio And Proportion Exercise 21

Question 1. I have taken measurement of the floor of my living room. I see that the rectangular floor is of 8 m length and 5 m in breadth. Let’s find the ratio of its length to its breadth. Let’s also write if the ratio is ratio of greater or lesser inequality.

Read and Learn More WBBSE Solutions For Class 6 Maths
Solution:

Length of the floor = 8 m.

Breadth of the floor = 5 m.

∴ Ratio of length and breadth = 8:5

It is a ratio of greater inequality.

Question 2. Sabita is making garlands of chinarose and marigold, if she made 12 garlands of chinarose and 15 of marigold, then let’s find what is the ratio of the number of garlands of chinarose and marigold. Let’s also write if the ratio is a ratio of greater or lesser inequality.
Solution:

Number of garlands of china rose = 12 and

Number of garlands of marigold = 15

∴ Ratio of garlands of qhinarose and marigold = 12:15 = 4:5

It is a ratio of lesser inequality.

Question 3. The ratio of my age to Sutapa’s age is 5: 6. If my age is 10 years, let’s find the age of Sutapa.
Solution:

The ratio of my age to Sutapa’s age = 5:6

or, \(\frac{\text { My age }}{\text { Sutapa’s age }}=\frac{5}{6}\)

or, \(\frac{10 \text { years }}{\text { Sutapa’s age }}=\frac{5}{6}\)

∴ 5 x Sutapa’s age = 6 x 10 years 6×10

∴ Sutapa’s age = \(\frac{6 \times 10}{5}\)  years = 12 years.

Class 6 WBBSE Math Solutions

Question 4. My mother gave sweets to me and Raju. Me and Raju ate sweets in the ratio of 1:3. Let’s find how many sweets my mother gave us [Let’s try any 4 values].

⇒ \(\frac{\text { No. of sweets I ate }}{\text { No. of sweets Raju ate }}=\frac{1}{3}=\frac{2}{6}\) i.e., mother gave (2 + 6) = 8 sweets also she can give (1 + 3) = 4 sweets

Solution:

\(\frac{\text { No. of sweets I ate }}{\text { No. of sweets Raju ate }}=\frac{1}{3}=\frac{2}{6}\) = \(\frac{3}{9}=\frac{4}{12}\)

In 1st case, mother gave us = 1 +3 = 4 sweets

In 2nd case, mother gave us = 2 + 6 = 8 sweets

In 3rd case, mother gave us = 3 + 9 = 12 sweets

In 4th case, mother gave us = 4 +12 = 16 sweets

Question 5. Today 10 of us have come to the park to play. If the ratio of number of girls and boys is 2:3 in our group, let’s find how many girls and boys have come to play.
Solution:

Total number of students = 10

Ratio of number of girls and boys = 2:3

∴ Number of girl students = 2/5 parts

∴ Number of boy students = 3/5 parts

Number of girl students = 2/5 x 10 = 4

Number of boy students = 3/5 x 10 = 6

Question 6. Father bought 4 pairs of bananas from market. If brother and sister ate those bananas in the ratio of 1 : 3, let’s find how many bananas each of them ate.
Solution:

Total number of bananas = 4 pairs = 4 x 2 = 8

Ratio of bananas brother and sister ate = 1:3

∴ Number of bananas brother ate = \(\frac{1}{1+3} \times 8=\frac{1}{4} \times 8=2\)

Number of bananas sister ate = \(\frac{3}{1+3} \times 8=\frac{3}{4} \times 8=6\)

Class 6 Maths Solutions WBBSE Chapter 21 Fundamental Concept Of Ratio And Proportion Exercise 21.1

Question 1. Let’s find if the following numbers are in proportion or not:

1. 13, 52,30,120
Solution:

1st term x 4th term = 13 x 120 = 1560

2nd term x 3rd term = 52 x 30 = 1560

∴ 13: 52 :: 30:120 (In proportion)

2. 22,11,72, 36
Solution:

1 st term x 4th term = 22 x 36 = 792

2nd term x 3rd term = 11 x 72 = 792

∴ 22: 11:: 72: 36 (In proportion)

3. 45, 27,15, 25
Solution: 45,27, 15,25

1st term x 4th term = 45 x 25 = 1125

2nd term x 3rd term = 27 x 15 = 405

∴ 1st term x 4th term  2nd term x 3rd term

∴ 45, 27,15, 25 are not in proportion.

Class 6 Maths Solutions WBBSE

4. 18, 20, 27, 30
Solution:

1st term x 4th term = 18 x 30 = 540

2nd term x 3rd term = 20 x 27 = 540

∴ 18: 20:: 27: 30 (In proportion)

5. 11,22, 36, 72
Solution:

1st term x 4th term = 11 x 72 = 792

2nd term x 3rd term = 22 x 36 = 792 (In proportion) .

Question 2. Let’s write if the folowing relations are True/False.

1. 4.5 litre: 13.5 litre:: 4 kg: 12 kg
Solution:

4.5 litre: 13.5 litre:: 4kg: 12 kg

4.5: 13.5:: 4: 12

1st term x 4th term = 4.5 x 12 = 54

2nd term x 3rd term = 13.4 x 4 = 54

∴ The relation is True.

Class 6 Maths Solutions WBBSE

2. 12 km: 8 km:: 61 km:: 40 km
Solution:

12 km: 8 km:: 60 km: 40 km

or, 12: 8:: 60: 40

1st term x 4th term = 12 x 40 = 480

2nd term x 3rd term = 8 x 60 = 480

∴ The relation is True.

3. 20 men: 45 men:: 180 rupee: 270 rupee
Solution:

20 men: 45 men:: 180 rupees: 270 rupees

∴ 1 st term x 4th term = 20 x 270 = 5400

2nd term x 3rd term = 45 x 180 = 8100

∴ 20:45 ≠ 180:270

∴ The relation is False.

4. 15m: 9m :: 35m: 21m.
Solution:

15m: 9 m :: 35 m: 21 m

or 15:9:: 35:21

1st term x 4th term = 15 x 21 = 315

2nd term x 3rd term = 9 x 35 = 315

∴ The relation is True.

WBBSE Math Solutions Class 6 Chapter 21 Fundamental Concept Of Ratio And Proportion Exercise 21.2

Question 1. Let’s find if the following numbers are in proportion or not. If they are in proportion, let’s write all the possible proportions with them.

1. 3,15, 4, 20
Solution:

1st case: 3, 15, 4, 20

1st term x 4th term = 3 x 20 = 60

2nd term x 3rd term = 15 x 4 = 60

∴ 3: 15:: 4.20

2nd case: 3, 4,15, 20

1st term x 4th term = 3 x 20 = 60

2nd term x 3rd term = 4 x 15 = 60

∴ 3:4:: 15: 20

3rd case: 15, 3, 20, 4

1st term x 4th term = 15 x 4 = 60

2nd term x 3rd term = 3 x 20 = 60

∴  15: 3:: 20: 4

4th case: 15, 20, 3, 4

1st term x 4th term = 15×4 = 60

2nd term x 3rd term = 20 x 3 = 60

∴ 15: 20:: 3: 4

WBBSE Math Solutions Class 6

2. 6,18,7, 21
Solution:

1st case: 6,18, 7, 21

1st term x 4th term = 6×21 = 126

2nd term x 3rd term = 18 x 7 = 126

∴ 6:18:: 7: 21

2nd case: 6, 7,18, 21

1st term x 4th term = 6 x 21 =126

2nd term x 3rd term = 7 x 18 = 126

∴ 6: 7:: 18: 21

3rd case: 18, 6, 21: 7

1st term x 4th term = 18 x 7 = 126

2nd term x 3rd term = 6 x 21 =126

∴ 18: 6:: 21: 7

4th case: 18, 21,6, 7

1st term x 4th term = 18 x 7 = 126

2nd term x 3rd term = 21 x 6 = 126

∴ 18: 21:: 6: 7

WBBSE Math Solutions Class 6

3. 5, 15, 7, 21
Solution:

1st case: 5,15, 7, 21

1st term x 4th term = 5 x 21 =105

2nd term x 3rd term = 15×7 = 105

∴ 5: 15:: 7: 21

2nd case: 15, 5, 21,7

1st term x 4th term = 15 x 7 = 105

2nd term x 3rd term = 5×21 =105

∴ 15: 5 :: 21: 7

3rd case: 5, 7, 15, 21

1st term x 4th term = 5 x 21 = 105

2nd term x 3rd term = 7 x 15 = 105

∴ 5:7:: 15: 21

4th case: 15, 21,5, 7

1st term x 4th term = 15 x 7 = 105

2nd term x 3rd term = 21 x 5 = 105

∴ 15:21:: 5: 7

4. 7, 21,4, 12
Solution:

1st case: 7, 21, 4,12

1st term x 4th term = 7 x 12 = 84

2nd term x 3rd term =21 x 4 = 84

∴ 7:21:: 4: 12

2nd Case: 21, 7,12, 4

1st x 4th term = 21 x 4 = 84

2nd term 3rd term = 7 x 12 = 84

∴ 21: 7:: 12: 4

3rd case: 7, 4, 21, 12

1st term x 4th term = 7 x 12 = 84

2nd term x 3rd term = 4×21 =84

∴  7:4:: 21: 12

4th case 21,12, 7, 4

1st term x 4th term = 21 x 4 = 84

2nd term x 3rd term = 12 x 7 = 84

∴ 21: 12:: 7: 4

WBBSE Class 6 Maths Solutions

5. 3,15,10,50
Solution:

1st case: 3, 15,10, 50

1st term x 4th term = 3 x 50 = 150

2nd term x 3rd term = 15 x 10 = 150

∴ 3: 15:: 10:50

2nd case: 15, 3, 50,10

1st term x 4th term = 15 x 10 = 150

2nd term x 3rd term = 3 x 50 = 150

∴ 15:3 :: 50:15

3rd case: 3, 10,15, 50

1st term x 4th term = 3 x 50 = 150

2nd term x 3rd term = 10×15=150

∴ 3: 10:: 15: 50

4th case: 15, 50, 3,10

1st term x 4th term = 15 x 10 = 150

2nd term x 3rd term = 50 x 3 = 150

∴ 15: 50:: 3: 10

6. 2, 6, 7, 21.
Solution:

1st case: 2, 6, 7, 21

1 st term x 4th term = 2 x 21 = 42

2nd term x 3rd term = 6 x 7 = 42

∴ 2:6:: 7: 21

WBBSE Class 6 Maths Solutions

2nd case: 6, 2, 21,7

1 st term x 4th term = 6 x 7 = 42

2nd term x 3rd term = 2 x 21 =42

∴ 6: 2:: 21: 7

3rd case: 2, 7, 6, 21

1st term x 4th term = 2 x 21 = 42

2nd term x 3rd term = 7 x 6 = 42

∴ 2: 7:: 6: 21

4th case: 6, 21,2, 7

1st term x 4th term = 6 x 7 = 42

2nd term x 3rd term = 21 x 2 = 42

∴ 6: 21:: 2: 7

Question 2. Let’s take 4 positive whole numbers:

1. 4,6,8,12
Solution:

1st case: 4, 6, 8, 12

1st term x 4th term = 4 x 12 = 48

2nd term x 3rd term = 6 x 8 = 48

∴ 4: 6:: 8: 12

2nd case: 6, 4,12, 8

1st term x 4th term = 6 x 8 = 48

2nd term x 3rd term = 4 x 12 = 48

∴ 6:4 :: 12:8

3rd case: 6,12, 4, 8

1st term x 4th term = 6 x 8 = 48

2nd term x 3rd term = 12 x 4 = 48

∴ 6:12 :: 4:8

4th case: 12, 6, 8, 4

1st term x 4th term = 12 x 4 = 48

2nd term x 3rd term = 6 x 8 = 48

∴12: 6:: 8:4

WBBSE Class 6 Maths Solutions

Question 3.

1. 3.5, 7, 2, 4
Solution: 3.5, 7, 2, 4

1st case: 3.5, 7, 2, 4

1st term x 4th term = 3.5 x 4 = 14

2nd term x 3rd term = 7×2 = 14

∴ 3.5: 7:: 2: 4

2nd case: 7, 3.5, 4, 2

1st term x 4th term = 7×2 = 14

2nd term x 3rd term = 3.5 x 4 = 14

∴ 7: 3.5:: 4:2

3rd case: 3.5, 2, 7, 4

1st term x 4th term = 3.5 x 4 = 14

2nd term x 3rd term = 2×7 = 14

∴ 3.5: 2:: 7: 4

4th case: 7,4, 3.5, 2

1st term x 4th term = 7×2 = 14

2nd term x 3rd term = 4 x 3.5 = 15

∴ 7: 4:: 3.5:2

2. 1.5, 4.5, 2.5; 7.5
Solution: 1.5, 4.5, 2.5, 7.5

1st case: 1.5, 4.5, 2.5, 7.5

1st term x 4th term = 1.5 x 7.5 = 11.25

2nd term x 3rd term = 4.5 x 2.5 = 11.25

∴ 1.5: 4.5:: 2.5: 7.5

2nd case: 4.5, 7.5,1.5, 2.5

1st term x 4th term = 4.5 x 2.5 = 11.25

2nd term x 3rd term = 7.5 x 1.5 = 11.25

∴ 4.5: 7.5:: 1.5:2.5

WBBSE Class 6 Maths Solutions

3rd case: 1.5, 2.5, 4.5, 7.5

1st term x 4th term = 1.5 x 7.5 = 11.25

2nd term x 3rd term = 2.5 x 4.5 = 11.25

∴1.5: 2.5:: 4.5 4.5: 4.5

4th case: 4.5,1.5, 7.5, 2.5

1st term x 4th term = 4.5 x 2.5 = 11.25

2nd term x 3rd term = 1.5 x 7.5 = 11.25

∴ 4.5: 1.5:: 7.5:2.5

3. 0.35,1.05, 0.09, 0.27
Solution: 0.35,1.05, 0.09, 0.27

1st case: 0.35,1.05,0.09, 0.27

1st term x 4th term = 0.35 x 0.27 = 0.0945

2nd term x 3rd term = 1.05 x 0.09 = 0.0945

∴ 0.35:1.05 :: 0.09:0.27

2nd case: 1.05, 0.35, 0.27, 0.09

1st term x 4th term = 1.05 x 0.09 = 0.0945

2nd term x 3rd term = 0.35 x 0.27 = 0.0945

∴ 1.05: 0.35:: 0.27: 0.09

3rd case: 0.35,1.05,0.09, 0.27

1st term x 4th term = 0.35 x 0.27 = 0.0945

2nd term x 3rd term = 1.05 x 0.09 = 0.0945

∴ 0.35:1.05 :: 0.09:0.27

WBBSE Class 6 Maths Solutions

4th case: 1.05,0.27,0.35, 0.09

1st term x 4th term = 1.05 x 0.09 = 0.0945;

2nd term x 3rd term = 0.27 x 0.35 = 0.0945

∴ 1.05: 0.27 ::0.35:0.09

4. Let’s take 4 positive decimal numbers:
Solution:

1st case: 2.4,4.8,7.5,15

Here, 1st term x 4th term = 2.4 x 15 = 36

2nd term x 3rd term F 4.8 x 7.5 = 36

= 2.4: 4.8:: 7.5:15

2nd case: 4.8, 2.4,15, 7.5

Here, 1 st term x 4th term = 4.8 x 7.5 = 36

2nd term x 3rd term = 2.4 x 15 = 36

∴ 4.8: 2.4:: 15:7.5

3rd case: 15, 7.5, 4.8, 2.4

Here, 1 st term x 4th term = 15 x 2.4 = 36

2nd term x 3rd term = 7.5 x 4.8 = 36

∴ 15:7.5:: 4.8 : 2.4

4th case: 2.4, 7.5, 4.8,15

Here, 1 st term x 4th term = 2.4 x 15 = 36

2nd term x 3rd term = 7.5 x 4.8 = 36

∴ 2.4: 7.5:: 4.8:15

Question 4.

1. \(\frac{1}{2}, \frac{1}{3}, \frac{1}{4}, \frac{1}{6}\)
Solution:

1st case: \(\frac{1}{2}, \frac{1}{3}, \frac{1}{4}, \frac{1}{6}\)

1st term x 4th term = \(\frac{1}{2} \times \frac{1}{6}=\frac{1}{12}\)

2nd term x 3rd term = \(\frac{1}{3} \times \frac{1}{4}=\frac{1}{12}\)

∴ \(\frac{1}{2}: \frac{1}{3}:: \frac{1}{4}: \frac{1}{6}\)

2nd case: \(\frac{1}{3}, \frac{1}{2}, \frac{1}{6}, \frac{1}{4}\)

1st term x 4th term = \(\frac{1}{3} \times \frac{1}{4}=\frac{1}{12}\)

2nd term x 3 rd term = \(\frac{1}{2} \times \frac{1}{6}=\frac{1}{12}\)

∴ \(\frac{1}{3}: \frac{1}{2}:: \frac{1}{6}: \frac{1}{4}\)

Class 6 Math WBBSE Solutions

3rd case: \(\frac{1}{2}, \frac{1}{4}, \frac{1}{3}, \frac{1}{6}\)

1st term x 4th term = \(\frac{1}{2} \times \frac{1}{6}=\frac{1}{12}\)

2nd term x 3rd term = \(\frac{1}{4} \times \frac{1}{3}=\frac{1}{12}\)

∴ \(\frac{1}{2}: \frac{1}{4}:: \frac{1}{3}: \frac{1}{6}\)

4th case: \(\frac{1}{3}, \frac{1}{6}, \frac{1}{2}, \frac{1}{4}\)

1st term x 4th term = \(\frac{1}{3} \times \frac{1}{4} \times=\frac{1}{12}\)

2nd term x 3rd term = \(\frac{1}{6} \times \frac{1}{2}=\frac{1}{12}\)

∴ \(\frac{1}{3}: \frac{1}{6}:: \frac{1}{2}: \frac{1}{4}\)

2. \(\frac{1}{5}, \frac{1}{10}, \frac{1}{16}, \frac{1}{32}\)

1st case: \(\frac{1}{5}, \frac{1}{10}, \frac{1}{16}, \frac{1}{32}\)

1st term  x 4th term = \(\frac{1}{5} \times \frac{1}{32}=\frac{1}{160}\)

2nd term x 3rd term = \(\frac{1}{10} \times \frac{1}{16}=\frac{1}{160}\)

∴ \(\frac{1}{5}: \frac{1}{10}:: \frac{1}{16}: \frac{1}{32}\)

2nd case: \(\frac{1}{10}, \frac{1}{5}, \frac{1}{32}, \frac{1}{16}\)

1st term x 4th term = \(\frac{1}{10} \times \frac{1}{16}=\frac{1}{160}\)

2nd term x 3rd term = \(\frac{1}{5} \times \frac{1}{32}=\frac{1}{160}\)

∴ \(\frac{1}{10}: \frac{1}{5}:: \frac{1}{32}: \frac{1}{16}\)

3rd case: \(\frac{1}{5}, \frac{1}{16}, \frac{1}{10}, \frac{1}{32}\)

1st term x 4th term = \(\frac{1}{5} \times \frac{1}{32}=\frac{1}{160}\)

2nd term x 3rd term = \(\frac{1}{16} \times \frac{1}{10}=\frac{1}{160}\)

∴ \(\frac{1}{5}: \frac{1}{16}:: \frac{1}{10}: \frac{1}{32}\)

Class 6 Math WBBSE Solutions

4th case: \(\frac{1}{10}, \frac{1}{32}, \frac{1}{5}, \frac{1}{16}\)

1st term x 4th term = \(\frac{1}{10} \times \frac{1}{16}=\frac{1}{160}\)

2nd term x 3rd term = \(\frac{1}{32} \times \frac{1}{5}=\frac{1}{160}\)

∴ \(\frac{1}{10}: \frac{1}{32}:: \frac{1}{5}: \frac{1}{16}\)

3. \(\frac{1}{3}, \frac{1}{6}, \frac{1}{9}, \frac{1}{18}\)

1st case: \(\frac{1}{3}, \frac{1}{6}, \frac{1}{9}, \frac{1}{18}\)

1st term x 4th term = \(\frac{1}{3} \times \frac{1}{18}=\frac{1}{54}\)

2nd term x 3rd term = \(\frac{1}{6} \times \frac{1}{9}=\frac{1}{54}\)

∴ \(\frac{1}{3}: \frac{1}{6}:: \frac{1}{9}: \frac{1}{18}\)

2nd case: \(\frac{1}{6}, \frac{1}{3}, \frac{1}{18}, \frac{1}{9}\)

1st term x 4th term = \(\frac{1}{6} \times \frac{1}{9}=\frac{1}{54}\)

2nd term x 3rd term = \(\frac{1}{3} \times \frac{1}{18}=\frac{1}{54}\)

∴ \(\frac{1}{6}: \frac{1}{3}:: \frac{1}{18}: \frac{1}{9}\)

3rd case: \(\frac{1}{3}, \frac{1}{9}, \frac{1}{6}, \frac{1}{18}\)

1st term x 4th term = \(\frac{1}{3} \times \frac{1}{18}=\frac{1}{54}\)

2nd term x 3rd term = \(\frac{1}{9} \times \frac{1}{6}=\frac{1}{54}\)

∴ \(\frac{1}{3}: \frac{1}{9}:: \frac{1}{6}: \frac{1}{18}\)

4th case: \(\frac{1}{6}, \frac{1}{18}, \frac{1}{3}, \frac{1}{9}\)

1st term x 4th term = \(\frac{1}{6} \times \frac{1}{9}=\frac{1}{54}\)

2nd term x 3rd term = \(\frac{1}{18} \times \frac{1}{3}=\frac{1}{54}\)

∴ \(\frac{1}{6}: \frac{1}{18}:: \frac{1}{3}: \frac{1}{9}\)

4. \(\frac{1}{8}, \frac{1}{24}, \frac{1}{5}, \frac{1}{15}\)
Solution:

1st case: \(\frac{1}{8}, \frac{1}{24}, \frac{1}{5}, \frac{1}{15}\)

1st term x 4th term = \(\frac{1}{8} \times \frac{1}{15}=\frac{1}{120}\)

2nd term x 3rd term = \(\frac{1}{24} \times \frac{1}{5}=\frac{1}{120}\)

2nd case: \(\frac{1}{24}, \frac{1}{8}, \frac{1}{15}, \frac{1}{5}\)

1st term x 4th term = \(\frac{1}{24} \times \frac{1}{5}=\frac{1}{120}\)

2nd term x 3rd term = \(\frac{1}{8} \times \frac{1}{15}=\frac{1}{120}\)

∴ \(\frac{1}{24}: \frac{1}{8}:: \frac{1}{15}: \frac{1}{5}\)

3rd case: \(\frac{1}{8}, \frac{1}{5}, \frac{1}{24}, \frac{1}{15}\)

1st term x 4th term = \(\frac{1}{8} \times \frac{1}{15}=\frac{1}{120}\)

2nd term x 3rd term = \(\frac{1}{5} \times \frac{1}{24}=\frac{1}{120}\)

∴ \(\frac{1}{8}: \frac{1}{5}:: \frac{1}{24}: \frac{1}{15}\)

4th case: \(\frac{1}{24}, \frac{1}{15}, \frac{1}{8}, \frac{1}{5}\)

1st term x 4th term = \(\frac{1}{24} \times \frac{1}{5}=\frac{1}{120}\)

2nd term x 3rd term = \(\frac{1}{15} \times \frac{1}{8}=\frac{1}{120}\)

∴ \(\frac{1}{24}: \frac{1}{15}:: \frac{1}{8}: \frac{1}{5}\)

5. \(\frac{1}{3}, \frac{1}{5}, \frac{1}{4}, \frac{3}{10}\)
Solution:

1st case: \(\frac{1}{3}, \frac{1}{5}, \frac{1}{4}, \frac{3}{10}\)

1st term x 4th term = \(\frac{1}{3} \times \frac{3}{10}=\frac{1}{20}\)

2nd term x 3rd term = \(\frac{1}{5} \times \frac{1}{4}=\frac{1}{20}\)

∴ \(\frac{1}{3}: \frac{1}{5} \neq \frac{1}{4}: \frac{3}{10}\)

∴ \(\frac{1}{3} \times \frac{1}{4}=\frac{1}{20}\)

4th case: \(\frac{1}{6}, \frac{1}{18}, \frac{1}{3}, \frac{1}{9}\)

1st term x 4th term = \(\frac{1}{6} \times \frac{1}{9}=\frac{1}{54}\)

2nd term x 3rd term = \(\frac{1}{18} \times \frac{1}{3}=\frac{1}{54}\)

∴ \(\frac{1}{6}: \frac{1}{18}:: \frac{1}{3}: \frac{1}{9}\)

Class 6 Math WBBSE Solutions

6. \(\frac{1}{8}, \frac{1}{24}, \frac{1}{5}, \frac{1}{15}\)

1st case: \(\frac{1}{8}, \frac{1}{24}, \frac{1}{5}, \frac{1}{15}\)

1st term x 4th term = \(\frac{1}{8} \times \frac{1}{15}=\frac{1}{120}\)

2nd term x 3rd term = \(\frac{1}{24} \times \frac{1}{5}=\frac{1}{120}\)

2nd case: \(\frac{1}{24}, \frac{1}{8}, \frac{1}{15}, \frac{1}{5}\)

1st term x 4th term = \(\frac{1}{24} \times \frac{1}{5}=\frac{1}{120}\)

2nd term x 3rd term = \(\frac{1}{8} \times \frac{1}{15}=\frac{1}{120}\)

∴ \(\frac{1}{24}: \frac{1}{8}:: \frac{1}{15}: \frac{1}{5}\)

3rd case: \(\frac{1}{8}, \frac{1}{5}, \frac{1}{24}, \frac{1}{15}\)

1st term x 4th term = \(\frac{1}{8} \times \frac{1}{15}=\frac{1}{120}\)

2nd term x 3rd term = \(\frac{1}{5} \times \frac{1}{24}=\frac{1}{120}\)

∴ \(\frac{1}{8}: \frac{1}{5}:: \frac{1}{24}: \frac{1}{15}\)

4th case: \(\frac{1}{24}\), \(\frac{1}{15}\), \(\frac{1}{8}\), \(\frac{1}{5}\)

1st term x 4th term = \(\frac{1}{24} \times \frac{1}{5}=\frac{1}{120}\)

2nd term x 3rd term = \(\frac{1}{15} \times \frac{1}{8}=\frac{1}{120}\)

∴ \(\frac{1}{24}: \frac{1}{15}:: \frac{1}{8}: \frac{1}{5}\)

7. \(\frac{1}{3}, \frac{1}{5}, \frac{1}{4}, \frac{3}{10}\)

1st case: \(\frac{1}{3}, \frac{1}{5}, \frac{1}{4}, \frac{3}{10}\)

1st term x 4th term = \(\frac{1}{3} \times \frac{3}{10}=\frac{1}{20}\)

2nd term x 3rd term = \(\frac{1}{5} \times \frac{1}{4}=\frac{1}{20}\)

∴ \(\frac{1}{3}: \frac{1}{5} \neq \frac{1}{4}: \frac{3}{10}\)

∴ \(\frac{1}{3} \times \frac{1}{4}=\frac{1}{20}\)

2nd case: \(\frac{1}{3}, \frac{1}{5}, \frac{3}{10}, \frac{1}{4}\)

= \(\frac{1}{5} \times \frac{3}{10}=\frac{3}{50}\)

∴ \(\frac{1}{3}: \frac{1}{5} \neq \frac{3}{10}: \frac{1}{4}\)

Again, \(\frac{1}{3} \times \frac{1}{4}=\frac{1}{12}, \frac{1}{5} \times \frac{3}{10}=\frac{3}{50}\)

∴ \(\frac{1}{3}, \frac{1}{5}, \frac{1}{4}, \frac{3}{10}\) are not in proportion.

8. \(\frac{8}{3}, 8, \frac{5}{3}, 8\)

1st case: \(\frac{8}{3} \times 8=\frac{64}{3}, 8 \times \frac{5}{3}=\frac{40}{3}\)

2nd case: \(\frac{8}{3} \times \frac{5}{3}=\frac{40}{.3}, 8 \times 8=64\)

∴ \(\frac{8}{3}, 8, \frac{5}{3}, 8\) are not in proportion.

Class 6 Math WBBSE Solutions Chapter 21 Fundamental Concept Of Ratio And Proportion Exercise 21.3

Question 1. Which of the following cases can be represented in ratio? Let’s write.

1. My friend Jatita’s weight and her height.
Solution: My friend Jatita’s weight and her height are not possible.

2. In this month, number of days I went to school and number of days my friend Jahir went to school.
Solution: In this month, the number of days I went to school and number of days my friend Jahir went to school — Possible.

3. The money I had and the money I spent.
Solution: The money I had and the money I spent — Possible.

4. Litres of water in my water bottle and temperature of water.
Solution: Litres of water in my water bottle and temperature of water — Not possible.

5. How long I played today and how long my brother played.
Solution: How long I play today and how long my brother played — Possible.

Question 2. Let’s express the following quantities in ratio and identify the ratio of greater inequality and the ratio of lesser inequality.

1. 10 kg, 15 kg.
Solution: 10 kg: 15 kg

= 10:15

= 2:3

(Ratio of lesser inequality).

2. 27 things and 18 things
Solution: 27 things: 18 things

= 27:18 = 3:2

(Ratio of greater inequality).

3. Rs. 30 and Rs. 22.50
Solution: Rs. 30: Rs. 22.50

= 30: 22.5

= 6 : 4.5 = 4:3

(Ratio of greater inequality).

4. 4.9 litre and 8.4 litre
Solution: 4.9 litre: 8.4 litre

= 4.9: 84

= 49 : 84

= 7:12

(Ratio of lesser inequality).

5. 52 m and 78 m
Solution: 52 m: 78 m = 52: 78

=4:6

= 2:3

(Ratio of lesser inequality).

6. 1 hr 24 mins and 6 hrs 18 min
Solution: 1 hr 24 min: 6 hr 18 min

= (60 + 24) min : (360 + 10) min = 84 min : 378 m

= 12:54

= 2:9

(Ratio of lesser inequality).

Question 3. A bamboo stick is 2 m long. 0.75 m of it is coloured red and rest part is colored white.
Solution:

Length of the bamboo stick = 2 m.

Portion of red colour = 0.75 m.

∴ Portion of white colour = (2 – 0.75) m = 1.25 m.

1. Let us find the ratio between the total length of bamboo and the portion painted red.
Solution: Length of bamboo: Length of red portion

= 2 : 0.75 = 2 : 75/100

= 2 : 3/4 = 8 : 3

2. Let’s find the ratio between the total length of bamboo and the portion painted white.
Solution: Length of bamboo: Length of white portion

= 2: 1.25 = 2: 125/100

= 2 : 5/4 = 8.5

3. Let’s find the ratio between the part coloured red and that coloured white.
Solution: Length of red portion: Length of white portion = 0.75:1.25

= 75:125

= 3:5

Class 6 Math Solutions WBBSE

Question 4. The ratio of length and breadth of my room is 7: 5. Let’s write 4 possible perimeters of the room in the above ratio.
Solution: Length: Breadth = 7:5

∴ \(\frac{\text { Length }}{\text { Breadth }}=\frac{7}{5}=\frac{14}{10}=\frac{28}{20}=\frac{56}{40}\)

  1. Perimeter = 2(7 + 5) = 2 x 12 = 24 units
  2. Perimeter = 2(14 + 10)= 2 x 24 = 48 units
  3. Perimeter = 2(28 + 20) = 2 x 48 = 96 units
  4. Perimeter = 2(56 + 40) = 2 x 96 = 192 units.

Question 5. I have 26 stamps. Myself and Mita shall divide the stamps in the ratio of 8: 5. Let’s find how many stamps each of us will have.
Solution:

Total number of stamps = 26

∴ \(\frac{\text { No. of Stamps of me }}{\text { No. of Stamps of Mita }}=\frac{8}{5}=8: 5\)

No. of Stamps of mine = 8/13 x 26 = 16

No. of stamps of Mita = 5/13 x 26 = 10

Question 6. The ratio of my textbooks and story books is 4:3. If number of textbooks are 28, let’s find the number of story books and a total number of books.
Solution:

The ratio of my textbooks and story books = 4:3

Total number of textbooks = 28.

∴ \(\frac{\text { No. of my text books }}{\text { No. of story books }}=\frac{4}{3}\)

or, \(\frac{28}{\text { No. of story books }}=\frac{4}{3}\)

4 x No. of story books = 3 x 28

No. of story books = \(\frac{3 \times 28}{4}\) = 21.

∴ Total number of books = No. of text books + No. of storybooks

= 28 + 21 = 49

Question 7. In a particular type of jewellery the ratio of gold and silver is 4: 7. In such type of jewelry ornament, how many milligrams of gold has been mixed with 357 milligrams of silver, it is to be calculated.
Solution:

Ratio of Gold and Silver = 4:7

∴ \(\frac{\text { Gold }}{\text { Silver }}=\frac{4}{7}\)

⇒ \(\frac{\text { Weight of Gold }}{\text { Weight of Silver }}=\frac{4}{7}\)

⇒ \(\frac{\text { Weight of Gold }}{357 \mathrm{mg}}=\frac{4}{7}\)

7 x weight of Gold = \(4 \times 357 \mathrm{mg}\)

Weight of Gold = \(\frac{4 \times 357}{7} \mathrm{mg} . \)

∴ Weight of Gold = 204 mg

Question 8. Let’s write the ratio of the three angles of an equilateral triangle.
Solution:

Each angle of an equilateral triangle = 60°

∴ 1st angle : 2nd angle : 3rd angle = 60°: 60°: 60°

= 1:1:1.

Class 6 Math Solutions WBBSE

Question 9. Let’s write the ratio of the angles of a right-angled isosceles triangle.
Solution:

The three angles of the right-angled isosceles triangle are 90°, 45°, and 45°.

∴ 1st angle : 2nd angle : 3rd angle = 90° : 45°, 45°

= 2:1:1 .

Question 10. Let me divide Rs. 210 among Fatema and Sakira in the ratio of 3:4. Let me find how much each would get.
Solution:

Total Amount = Rs. 210.

Amount of Fatema: Amount of Sakira = 3:4

∴ Amount of money Fatema received

Amount of money Sakira received = Rs. (210 – 90) = Rs. 120.

Question 11. Mohit bought 6 bananas for Rs. 18 from a vendor and Raju bought 2 dozen of bananas for Rs. 72 from another vendor. Let’s express in ratio to find who paid more for bananas.
Solution:

Mohit bought 6 bananas for Rs. 18.

∴ Mohit bought 1 banana for Rs. 18/6 = Rs. 3.

Raju bought 2 dozen (24) bananas for Rs. 72.

∴ Raju bought 1 banana for Rs. 72/24 = Rs. 3.

∴ Ratio of prices = 3:3 = 1 :1 (Equal amount)

Question 12. The distances of Ayesha and Kamal’s house from our school are 1 km and 600 m respectively. Today Ayesha and Kamal came to school in 20 min and 12 min respectively. Let’s find, expressed in ratios, if they reached school at the same time or one of them has reached earlier.
Solution:

Distance of Ayesha’s house from school: Distance of Kamal’s house from school

= 1 km : 600 m

= 1000 m: 600 m = 5:3

Again, time taken by Ayesha: time taken by Kamal = 20 min: 12 min

= 5:3

∴ Their speeds are equal.

Question 13. Let’s find which of the following ratios are equal ratios

1. 3:3 and 5:5
Solution: = 1: 1 and 1: 1

∴ Equal ratio

2. 20 : 24 and 25 : 30
Solution: 20: 24 and 25: 30

= 5: 6 and 5: 6.

∴ Equal ratio.

3. 1: 9 and 9:18
Solution: 1:9 and 9: 18

= 1: 9 and 1: 2

∴ Not equal ratio

4. 28 : 21 and 20:15
Solution: 28:21 and 20:15

= 4 : 3 and 4 : 3

∴ Equal ratio

5. 1.4: 0.6 and 6.3 : 2.7
Solution: 1.4 : 0.6 and 6.3 : 2.7

= 14 : 6 and 63 : 27

= 7 : 3 and 7 : 3

∴ Equal ratio

6. 52 : 39 and 44 : 33
Solution: 52: 39 and 44: 33

= 4 : 3 and 4 : 3

∴ Equal ratio

Question 14. Let’s verify which of the following numbers are in proportion:

1. 9, 7, 36, 28
Solution: 9, 7, 36, 28

1st term x 4th term = 9 x 28 = 252

2nd term x 3rd term = 7 x 36 = 252

∴ 9, 7, 36, and 28 are in proportion.

2. 12, 30,14, 70
Solution: 12, 30, 14, 70

1st term 4th term = 1 2 x 70 = 840

2nd term x 3rd term = 30 x 1 4 = 420

∴ 12, 30, 14, 70 are not in proportion.

3. 24, 6, 108, 27
Solution: 24, 6, 108, 27

1st term x 4th term = 24 x 27 = 648

2nd term x 3rd term = 6 x 1 08 = 648

∴ 24, 6, 108, 27 are in proportion.

4. \(\frac{1}{2}, 1, \frac{3}{5}, 1 \frac{1}{5}\)
Solution: \(\frac{1}{2}, 1, \frac{3}{5}, 1 \frac{1}{5}\)

= \(\frac{1}{2}, 1, \frac{3}{5}, \frac{6}{5}\)

1st term x 4th term = \(\frac{1}{2} \times \frac{6}{5}=\frac{3}{5}\)

2nd term x 3rd term = \(1 \times \frac{3}{5}=\frac{3}{5}\)

∴ \(\frac{1}{2}, 1, \frac{3}{5}, 1 \frac{1}{5}\) are in proportion.

5. 72, 45, 70, 25
Solution: 72, 45, 70, 25

1st term x 4th term = 72 x 25 = 1800

2nd term x 3rd term = 45 x 70 = 31 50

∴ 72, 45, 70, 25 are not in proportion

6. _______ Let’s take + positive whole numbers.
Solution: 7, 8, 35, 40

1 st term x 4th term = 7 x 40 = 280

2nd term x 3rd term = 8 x 35 = 280

∴ 7, 8, 35, 40 are in proportion.

Class 6 Math Solutions WBBSE

Question 15. Let’s first try to find, if the following numbers are in proportion, let’s find all other possible proportions for each of them.

1. 60, 2,10,12
Solution: 60, 2,10,12

Case 1: Here, 1st term x 4th term = 60 x 12 = 720

2nd term x 3rd term = 2 x 10 = 20

∴ 60: 2 ≠10: 12

Case 2: 60, 12, 10,2

Here, 1st term x 4th term = 60 x 2 = 120

2nd term x 3rd term = 12 x 10 = 120

∴ 60: 12 :: 10: 2

Case 3: 60, 12,12, 2

Here, 1 st term x 4th term = 60 x 2 = 120

2nd term x 3rd term = 10 x 12 = 120

∴ 60 : 10 :: 12 : 2

Case 4: 10,2,60, 12

Here, 1 st term x 4th term = 10 x 12 = 120

2nd term x 3rd term = 2 x 60 = 120

∴ 10: 2:: 60: 12

2. 4,10, 6,15
Solution: 4,10, 6,15

Case 1: 4, 10, 6,15

Here, 1 st term x 4th term = 4 x 15 = 60

2nd term x 3rd term = 6 x 10 = 60

∴ 4 : 10 :: 6: 15

Case 2: 4, 6,10, 15

Here, 1 st term x 4th term = 4 x 15 = 60

2nd term x 3rd term = 6 x 10 = 60

∴ 4 : 6:: 10 : 15

Case 3: 60, 10, 12,2

Here, 1st term x 4th term = 10 x 6

60 2nd term x 3rd term = 4 x 15 = 60

∴ 10 : 4:: 15 : 6

Case 4: 10, 15, 4,6

Here, 1st term x 4th term = 10 x6 = 60

2nd term x 3rd term = 15 x 4 = 60

∴ 10: 15:: 4: 6

3. 8, 9, 24, 2
Solution: 8, 9, 24, 2

Case 1: 8, 24, 2, 9

Here, 1 st term X 4th term = 8 x 9 = 72

2nd term x 3rd term = 24 x 2 = 48

∴ 8: 24 ≠ 2: 9

Case 2: 8, 9, 2, 24

Here, 1st term x 4th term = 8 x 24 = 192

2nd term x 3rd term = 9×2 = 18

∴ 8: 9 ≠ 2: 24

Case 3: 8, 24, 9, 2

Here, 1st term x 4th term = 8×2 = 16

2nd term x 3rd term = 24 x 9 = 216

∴ 8 : 24 ≠ 9:2

∴ 8, 9, 24, 2 are not in proportion

4. 3, 5,15, 25
Solution: 3, 5, 15, 25

Case 1: 5, 3, 25, 15

Here, 1 st term x 4th term = 5 x 15 = 75

2nd term x 3rd term = 3 x 25 = 75

∴ 5 : 3:: 25 :15

Case 2: 5, 25, 3, 15

Here, 1 st term x 4th term = 5 x 15 = 75

2nd term x 3rd term = 25 x 3 = 75

∴ 5: 25 :: 3:15

Case 3: 25, 5, 15, 3

Here, 1st term x 4th term = 25 x 3 = 75

2nd term x 3rd term = 5×15 = 15

∴ 10: 4:: 15:6

Case 4: 25,15, 5, 3

Here, 1st term x 4th term = 25 x 3 = 75

2nd term x 3rd term = 15 x 5 = 75

∴ 25 : 15 :: 5 : 3

5. 45, 5,75,5

Solution: 45, 5, 75: 5

Here, 45 x 5 = 225 75 X 5 = 375

∴ 45:5 ≠ 75.5

Again, 45 x 75 5 x 5 = 25

∴ 45 : 5 ≠ 5: 75

∴ 45, 5, 75, and 5 are not in proportion.

6. 24, 4, 36, 6
Solution: 24, 4, 36, 6

Case 1: 24, 4, 36, 6

Here, 1 st term x 4th term = 24 x 6 = 144

2nd term x 3rd term = 4 x 36 = 144

∴ 24 : 4:: 36 : 6

Case 2: 24, 36, 4, 6

Here, 1st term x 4th term = 24 x 6 = 144

2nd term x 3rd term = 36 x 4 = 144

∴ 24 : 36 :: 4: 6

Case 3: 4, 24, 6, 36

Here,. 1 st term x 4th term = 4 x 36 = 144

2nd term x 3rd term = 24 x 6 = 144

∴ 4: 24 6: 36

Case 4: 4, 6, 24, 36

Here, 1 st term x 4th term = 4 x 36 = 144

2nd term x 3rd term = 6 x 24 = 144

∴ 4:6:: 24 : 36

Class 6 Math Solutions WBBSE

Question 16. The height of my friend Priya is 160 cm and the height of her mother is 170 cm. Again, Priya’s weight is 40 kg and her mother’s weight is 42.5 kg. Let’s find if their weights are in proportion to their heights.
Solution:

Height of Priya = 160 m.

Height of Priya’s mother = 170 m.

∴  Ratio of their heights = 160 m: 170 m.

= 16:17

Again, weight of Priya = 40 kg.

Weight of Priya’s mother = 42.5 kg.

∴ Ratio of their weights = 40 kg: 42.5 kg.

= 40: 425/10

= 16:17

∴ Their weights are in proportion to their heights.

 

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root

Class 6 Math Solutions WBBSE Chapter 18 Square Root Exercise 18

Question 1. 441 oranges were picked from Nisar’s fruit garden. Oranges are to be kept in a basket. Each basket will contain as many oranges as there are a number of baskets. Let’s calculate to find the number of baskets.
Solution:

Total number of oranges = 441

No. of baskets = \(\sqrt{441}=\sqrt{21 \times 21}=21\)

Question 2. Today morning I arranged the books in the almirah of my room. In each shelf, I arranged books equal to the number of shelves of the almirah. But 5 books remained out of the almirah. If total number of books are 86, let’s find the number of shelves of the almirah.
Solution:

Total number of books = 86.

But 5 books remained out of the almirah.

∴ Total number of books in the aimirah = 86 – 5 = 81.

∴ Number of shelves of the aimirah = \(\sqrt{81}=\sqrt{9 \times 9}=9\)

Read and Learn More WBBSE Solutions For Class 6 Maths

Question 3. In the playground, we decided to arrange ourselves and stand in a square form. After some have formed this square, it’s found that 4 friends are staying apart. If they join the square, it will not remain square anymore. 40 students are present today in our class. Let’s calculate in this arrangement how many students are there in each row.
Solution:

Number of students present today = 40.

To make a square form 4 students will be excess.

∴ Number of students required to make a square form = 40 – 4 = 36.

∴ Number of students is each row = \(\sqrt{36}=\sqrt{6 \times 6}=6\)

Class 6 Math Solutions WBBSE

Question 4. In the Sukanta Memorial Library of our locality, the members contributed as many rupees as there are members. If the total collection is Rs. 729 let’s find the number of members of the library.
Solution:

Total collections from the members = Rs. 729

As each members contribute as many rupees as there are members.

∴ Number of members = \(\sqrt{729}=\sqrt{3 \times 3 \times 3 \times 3 \times 3 \times 3}\)

Question 5. To dig a pond in Raghunathpur village, the number of people employed worked for as many numbers of days as there were number of people working, and got as payment Rs. 12375.
Solution:

Number of people working and get as payment Rs 12375.

If each, gets daily wage of Rs. 55.

Number of people joined the work  =\(\sqrt{\frac{12375}{55}}=\sqrt{225}=\sqrt{15 \times 15}=15\)

Class 6 Math Solutions WBBSE

Question 6. If each gets a daily wage of Rs. 55 then let’s find how many pepole joined the work.
Solution:

The total money collected = Rs. 4096.

As each member paid an amount 4 times the number of members.

∴ Number of members went for the trip

= \(\frac{\sqrt{4096}}{4}=\sqrt{1024}=\sqrt{4 \times 4 \times 4 \times 4 \times 2 \times 2}\)

= 4x4x2 = 32

Question 7. Today is Children’s Day. Few of us distributed toffee and biscuits among the other students of the school. But 800 toffees were left. So each took twice the number of toffees as we are in number. Let’s calculate among how many of us those 800 toffees were divided.
Solution:

Each took twice the number of toffees as we are in number.

800 toffee were left.

∴ Number of children = \(\sqrt{\frac{800}{2}}=\sqrt{400}=\sqrt{20 \times 20}=20\)

Question 8. Safikul uncle of Atla village brought 780 saplings of papaya tree. He decided to plant them in as many rows as there are number of plants in each row. But by trying to do, he fell short of 4 saplings. In how many rows did Rafikul’s uncle decide to plant the saplings, let’s find. Solution:

The number of saplings of the papaya tree = 780 He fell short of 4 saplings.

∴ Total number of saplings required = 780 + 4 = 784

∴ Number of rows = \(\sqrt{784}=\sqrt{4 \times 4 \times 7 \times 7}\) = 4 x 7 = 28.

Class 6 Math Solutions WBBSE

Question 9. I made a square cardboard box which has many square cells. Each row has many cells as there are a number of rows. My brother kept one 5 rupee, one two rupee, and a one rupee coin in each cell. If total money kept is Rs. 1152, then let’s find how many cells there are in each row of may cardboard box.
Solution:

The total money kept is Rs. 1152.

My brother kept one 5 rupee, a two rupee and a one rupee coin in each cell.

∴ Number of cells = \(\sqrt{\frac{1152}{5+2+1}}=\sqrt{\frac{1152}{8}}\)

= \(\sqrt{144}=\sqrt{12 \times 12}=12\)

Question 10. Let’s find the value of the following

1. Square of 7 = ____
Solution: Square of 7 = 7 x 7 = 49

2. Square root of 121 = _______
Solution: Square root of 121 = √121

= \(\sqrt{11 \times 11}=11\)

3. 9² = _______
Solution: 92 = 9 x 9 = 81

4. √100 = ______
Solution: \(\sqrt{100}=\sqrt{10 \times 10}=10\)

5. √49 = _________
Solution: \(\sqrt{49}=\sqrt{7 \times 7}=7\)

6. √144 = ______
Solution: \(\sqrt{144}=\sqrt{12 \times 12}=12\)

7. \(\sqrt{3^2 \times 2^2}\) = ________
Solution: \(\sqrt{3^2 \times 2^2}=\sqrt{9 \times 4}\)

= \(\sqrt{36}=\sqrt{6 \times 6}=6\)

8. \(\sqrt{5 \times 7 \times 5 \times 7}\) = ________
Solution: \(\sqrt{5 \times 7 \times 5 \times 7}=\sqrt{5^2 \times 7^2}\) = 5 x 7 = 35

9. \(\sqrt{13 \times 13}\) = _____
Solution: \(\sqrt{13 \times 13}\) = 13

Class 6 WBBSE Math Solutions

Question 11. Let’s find the square root of the following by finding factors

1. 169
Solution: \(\sqrt{169}=\sqrt{13 \times 13}=13\)

2. 225
Solution: \(\sqrt{225}=\sqrt{15 \times 15}=15\)

3. 4² + 3²
Solution: \(\sqrt{4^2+3^2}=\sqrt{16+9}\)

= \(\sqrt{25}=\sqrt{5 \times 5}=5\)

4. √144
Solution: \(\sqrt{144}=\sqrt{12 \times 12}=12\)

5. 576
Solution: \(\sqrt{576}=\sqrt{4 \times 4 \times 6 \times 6}\) = 4 x 6 = 24

6. 15² + 20²
Solution: \(\sqrt{15^2+20^2}=\sqrt{225+400}\)

= \(\sqrt{625}=\sqrt{5 \times 5 \times 5 \times 5}\)

= \(5 \times 5=25\)

7. 900
Solution: \(\sqrt{900}=\sqrt{3 \times 3 \times 10 \times 10}\)

Class 6 WBBSE Math Solutions Chapter 18 Square Root Exercise 18.1

Question 1. Let’s find if 108, 64,162, 81 are square numbers or not let us find the smallest whole number other than ‘0’ with which these should be multiplied or divided to give a square number.

1. 108
Solution:

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root 108 Is Not A Square Number

108 = 2x2x3x3x3

∴ 108 is not a square number.

If 3 is multiplied or divided with 108, it will be a square number.

∴ 108 x 3 = 324, a square number or, 108 ÷ 3 = 36, a square number

2. √64
Solution:

= \(\sqrt{2 \times 2 \times 2 \times 2 \times 2 \times 2}\)

=2x2x2=8

∴ 64 is a square number.

3. 162
Solution:

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root 162 Is Not A Square Number

∴162 = 3x3x3x3x2

∴ 162 is not a square number.

If 2 is multiplied or divided with 162, it will be a square number.

∴ 162 x 2 = 324 = 18 x 18, a square number,

or, 162 ÷ 2 = 81 = 9 x 9, a square number.

4. √81
Solution:

= \(\sqrt{3 \times 3 \times 3 \times 3}\) =3×3 = 9

∴ 81 is a square number.

Class 6 Maths Solutions WBBSE Chapter 18 Square Root Exercise 18.2

Question 1. Apart from 0, by which least whole number the following numbers must be divided to get square numbers

  1. 845
  2. 450
  3. 18 x 6
  4. 25 x 35

1. 845
Solution:

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root 845 Is Not A Square Number

845 = 13x13x5

Hence, it is not a square number.

If we divide the number by 5, we will get a square number.

∴ The required number is 5.

2. 450
Solution:

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root 450 Is Not A Square Number

∴ 450 = 5x5x3x3x2

Hence, it is not a square number, if we divide the number by 2, it will be a square number.

∴ The required number is 2.

Class 6 Maths Solutions WBBSE

3. 18×6
Solution:

= (3 x 3 x 2) x (2 x 3)

=3x3x2x2x3

Hence, it is not a square number, if we divide the number by 3, it will be a square number.

∴ The required number is 3.

4. 25 x 35 = (5 x 5) x (5 x 7)
Solution:

Hence, it is not a square number, if we divide the number by 35 (5 x 7), it will be a square number.

∴ The required number = 35.

Question 2. By which least whole number apart from 0, the following numbers should be multiplied to give a square number:

1. 432
Solution:

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root 432 Is Not A Square Number

=2x2x3x7x7x3

Hence, 588 is not a square number, if we multiply 3 with it, it will be a square number.

∴ The required number is 3.

Class 6 Maths Solutions WBBSE

2. 588
Solution:

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root 588 Is Not A Square Number

= 2x2x3x7x7x3

Hence 588 is not a square number, if we multiply 3 with it, it will be a square number.

∴ The required number is 3

3. 25×20
Solution:

= 5x5x2x2x5

Hence, it is not a square number, if we multiply 5 with it, it will be a square number.

∴ The required number is 5.

4. 24x 28
Solution:

=2x2x2x3x2x2x7

Hence, it is not a square number, if we multiply 2x3x7 with it, it will be a square number.

∴ The required number is 2 x 3 x 7 = 42.

WBBSE Math Solutions Class 6 Chapter 18 Square Root Exercise 18.3

Question 1. Let’s work out to find the least square number other than 0, which is divisible by 12,16, 20, and 24.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root LCM Of 12, 16, 20, 24

∴ L.C.M.of 12, 16, 20 and 24 = 2x2x2x2x3x5 = 240

Hence, 240 is not a least square number

If we multiplied 240 by 3 x 5, then it will be the least square number.

∴ The required least square number.

= 240 x 3 x 5 = 3600.

WBBSE Math Solutions Class 6

Question 2. The product of two positive whole numbers is 98 and the greater one is twice the smaller number. Let’s find the two numbers.
Solution:

Greater number = 2x smaller number

Greater number x smaller number = 98

or, (2 x smaller number) x smaller number = 98

or, 2 x (smaller number)² = 98

∴ (Smaller number)² = 98/2 = 49

∴ Smaller number = √49 =7

∴ Greater number = 2 x smaller number = 2×7 = 14

∴ The required numbers are 7 and 14.

Question 3. Let’s find which least square number has factor 17.
Solution: The least square number which has a factor =17×17 = 289

Question 4. Let’s find the least square number other than 0 which is divisible by 10,15,20 and 30. Also, let’s write the next square number which will be divisible by these numbers.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root LCM Of 10, 15, 20, 30

∴ L.C.M. = 2x2x3x5 = 60

It is not a square number. If we multiplily by 3 x 5, we will get a square number.

∴ Least square number = 60 x 3 x5 = 900.

∴ The next square number = 900 x 4 = 3600.

WBBSE Math Solutions Class 6

Question 5. Let’s analyse the given numbers and place them in their respective columns-20, 27, 50, 75, 100, 108,144, 169,180, 256
Solution:

20 = 2 x 2 x 5 – it is not a square number

27 = 3 x 3 x 3 – it is not a square number

50 = 5 x 5 x 2 – it is not a square number

75 = 5 x 5 x 3 – it is not a square number

100 = 2 x 2 x 5 x 5 – it is a square number

108 = 6 x6 x 3 – it is not a square number

144 = 2 x 2 x 6 x 6 – it is a square number

169 = 13 x 13 – it is a square number

180 = 2 x 2 x 3 x 3 x 5 – it is not a square number

256 = 4 x 4 x 4 x 4 – it is a square number

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root

Question 6. This year on Netaji’s birthday, the students present in Physical Education class were made to stand in rows of 18,24,27, at different points of time, to march past At one point of time we formed a solid square. Let us find the least number of students present in school on that day.
Solution: L.C.M of 18, 24, 27

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root LCM Of 18 24 27

= 2 x 2 x 2 x 3 x 3 x 3

= 216

It is not a square number, if we multiply 2×3 with it, it will be a square number.

∴ Least number of students = 216x2x3 = 1296

WBBSE Math Solutions Class 6

Question 7. The product of two positive numbers is 147. The greater number is 3 times the smaller number. Let’s find the numbers.
Solution:

Greater number = 3 x smaller number .

Greater number x smaller number = 147

or, 3 x smaller number x smaller number = 147

or, (Smaller number)² = 147/3 = 49

∴ Smaller number = √49 = 7

Greater number = 3×7 = 21.

Question 8. Arrange the following in ascending order of their value:

⇒ \((\sqrt{36}+\sqrt{25}),(\sqrt{49}+\sqrt{9}) ;(\sqrt{25}+\sqrt{100}),(\sqrt{4}+\sqrt{16})\)

Solution:

⇒ \((\sqrt{36}+\sqrt{25})\)

= 6 + 5 = 11

⇒ \((\sqrt{49}+\sqrt{9})\)

= 7 + 3 = 10

⇒ \((\sqrt{25}+\sqrt{100})\)

= 5 + 10 = 125

⇒ \(\sqrt{4}+\sqrt{16}\)

= 2 + 4 = 6

In ascending order

6 ∠ 10 ∠ 11 ∠ 15

i.e., \(\sqrt{4}+\sqrt{16} ; \sqrt{49}+\sqrt{9} ; \sqrt{36}+\sqrt{25} ; \sqrt{25}+\sqrt{100}\)

WBBSE Class 6 Maths Solutions

Question 9. Of three positive numbers, the product of first and second is 24 second and third is 48 and that of first and third is 32. Let’s find the three numbers.
Solution:

1st number x 2nd number = 24

2nd number x 3rd number = 48

1st number x 3rd number = 32

(1st number x 2nd number) x (1st number x 3rd number)/ (2nd number x 3rd number)

∴ (1st number)² = 16

∴ 1st number = √16 = 4

Again, 1st number x 2nd number = 24

or, 4 x 2nd number = 24

∴ 2nd number = 24/4 = 6

Again, 2nd number x 3rd number = 48

6 x 3rd number = 48

∴ 3rd number = 48/6 = 8

∴ Required numbers are 4, 6, and 8.

Question 10. On Republic Day, our Physical Education teacher made all students stand in rows having 12,15, and 20 students, at different points of time, for march past. At one point of time, the students were arranged in solid square. Let’s find out at least how many students were present in school on that day.
Solution:

L.C.M. of 12, 15 and 20

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root LCM Of 12 15 20

= 2 x 2 x 3 x 5

But 60 is not a square number, if we multiply 3 and 5 with it, it will be square number.

∴ The required number = 60 x 3 x 5 = 900.

WBBSE Class 6 Maths Solutions Chapter 18 Square Root Exercise 18.4

Question 1. Let’s find the square number nearest to 1000.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root Nearest To 1000 Square Root

∴ 1000 – 39 = 961 is a square number.

∴ √961 = 31

Next square number is (32)² = 1024

1024- 1000 = 24 ∠ 39

∴ Square number nearest to 1 000 is 1024.

Question 2. Let’s find the least number that will be subtracted from 9585 to give a square number.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root 9585 Least Number

∴ The required number is 176.

Question 3. Let’s find what least number must be added to 5320 to make it a perfect square.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root Least Number Subtracted From 5320 Is 9

Next square number is (73)² = 5329.

∴ The required number that is to be added to 5320 to make a square number is 5329-5320 = 9.

Class 6 Math WBBSE Solutions

Question 4. Let’s find the least square number other than 0, which is divisible by 15, 25, 35, 45.
Solution:

L.C.M.of 15,25, 35 and 45

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root LCM Of 15 25 35 And 45

= 3x5x5x7x3 = 1575.

It is not a square number, if we multiply 7 with it, it will be a square number.

∴ The required least square number = 1575 x 7 = 11025.

Question 5. Let’s find the least square number of 4 digits which are divisible by 8, 15, 20, and 25.
Solution:

L.C.M. of 8, 15, 20 and 25

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root LCM Of 8 15 20 And 25

= 2 x 2 x 5 x 2 x 3 x 5 = 600

If we multiply 600 by 2 and 3 then we get a square number.

∴ The least-square number of 4 digits = 600 x 6 = 3600.

Question 6. Let’s find the least square number of 4 digits.
Solution:

The least 4 digit number is 1000.

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root The Least Four Digit Number Is 1000

1000- 39 = 961 is a square number.

√961 =31

Next square number = (32)² = 1 024.

∴ Least square number of 4 digits = 1 024.

Class 6 Math WBBSE Solutions

Question 7. Let’s find the greatest square number of 4 digits.
Solution:

The greatest number of 4 digits = 9999.

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root The Greatest Square Of Four Digit Number Is 9801

The greatest square number of 4 digits = 9999 -198 = 9801.

Question 8. Let us find the square root of the following by the method of division:
Solution:

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root Square Root By The Division Method

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root Square Root By The Division Method-1

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root Square Root By The Division Method-2

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root Square Root By The Division Method-3

Question 9. Without finding square root, let us find the possible digits in unit’s place and number of digits in the square root number:

1. 784
Solution:

Possible digits in unit’s place = 2, 4

∴ Number of digits in the square root number = 2

Class 6 Math WBBSE Solutions

2. 3676
Solution:

Possible digits in 4 unit’s place = 6

∴ Number of digits in the square root number = 2

3. 160000
Solution:

Possible digits in unit’s place = 0

Number of digits in the square root number = 3

4. 1225
Solution:

Possible digits in unit’s place = 5

∴ Number of digits in the square root number = 2

5. 2401
Solution:

Possible digits in unit’s place = 1,9

∴ Number of digits in the square root number = 2

6. 10201
Solution:

Possible digits in unit’s place =,1,9.

∴ Number of digits in the square root number = 3

Question 10. Let’s find two square numbers nearest to 5000.
Solution: 5000

WBBSE Solutions For Class 6 Maths Chapter 18 Square Root Two Square Numbers Nearest To 5000

Nearest to 5000 = (70)² and (71)²

= 4900 and 5041

Question 11. The product of two numbers is 1576 and their quotient is 9/7, let’s find the numbers.
Solution:

1st number x 2nd number = 1575

and \(\frac{1 \text { st number }}{2 \text { nd number }}=\frac{9}{7}\)

∴ \((1 \text { st number } \times 2 \text { nd number }) \times \frac{1st number }{2nd num ber}=1575 \times \frac{9}{7}\)

∴ (1st number)² = 225 x

1st number = \(\sqrt{225 \times 9}\) = 15 x 3 = 45

∴ 2nd number = 1575 ÷ 45 = 35

∴ The numbers are 45, 35.

Question 12. Let us find what digit will be placed in * of 202*, so that it becomes a square number.
Solution: 202 *

1 st if we put 1, then 2021 is not a square number.

2nd if we put 2, then 2022 is not a square number.

3rd if we put 3, then 2023 is not a square number.

4th, if we put 4, then 2024 is not a square number.

5th if we put 5, then 2025 is a square number.

∴ The required digit is 5.

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box

Class 6 Math Solutions WBBSE Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Exercise 17

Question 1. I myself drew a quadrilateral and a triangle with the help of scale. I also measured their sides with the scale.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Quadrilateral Scale

ABCD is a quadrilateral whose AB = 7 cm, BC = 1.8 cm, CD = 5 cm. and DA = 4 cm.

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Triangle Scale

PQR is a triangle whose PQ = 4.5 cm, QR = 6 cm, and RP = 5.4 cm.

Read and Learn More WBBSE Solutions For Class 6 Maths

Question 2. I have drawn two line segments of length 2.8 cm, and 5.3 cm, and named them.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Two line Segments

MN is a line segment whose length = 2.8 cm and EF is another line segment whose length = 5.3 cm.

Class 6 WBBSE Math Solutions Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Exercise 17.1

Question 1. Let’s draw a line segment of length 4.5 cm with scale and divider.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Line Segment Of Length 4.5 cm With Scale

PR is a line segment whose length is 4.5 cm.

Question 2. From a straight line let’s mark out a length – XY equal to 6 cm.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Straigth Line Length XY Equal To 6 cm

Question 3. Using scale and divider, let’s draw two line segments of length 6 cm and 5.7 cm, and name them.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Scale And Divider Of Two Line Segments

Question 4. Using scale and divider let us draw two line segments AB and CD of lengths 3.6 cm and 2.2 cm.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Two line Segments Length 3.6 cm and 2.2 cm

Class 6 WBBSE Math Solutions

Question 5. On a straight line, let’s draw a line segment XY which is the sum of the line segments AB and CD marked with a divider separately on the line. On another straight line, the segments AB and CD are separately marked in a way with a divider such that the line segment EF is the difference of the line segments AB and CD.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Straigth Line Length XY Which Is The Sum Of AB And CD

Question 6. Using scale and compass and taking two separate points as centres let is draw two circles having radii of lengths 3.2 cm and 2.9 cm
Solution:

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Scale ANd Compass And Taking Two Separate Points Centres

Class 6 WBBSE Math Solutions

Question 7. Let’s measure and write the values of the angles given below with a protractor. Let’s identify the angles as acute angle or right angle obtuse angle straight angle or reflex angle and arrange them in the increasing order of their values.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Identify The Angles

  1. ∠ACB = 40°; (Acute angle)
  2. ∠CDE = 180° (Straight angle)
  3. ∠JLK = 120° (Obtuse angle)
  4. ∠PQR = 30° (Acute angle)

Reflex Z PQR = 360°-30° = 330°

  1. ∠IJH = 120° (Obtuse angle)
  2. ∠FEG = 90° (Right angle)
  3. ∠YXZ = 30° (Acute angle)
  4. ∠XYZ = 140° (Obtuse angle)

Class 6 WBBSE Math Solutions

Question 8. Let’s write the sides and the vertex for each of the following angles.
Solution:

1. Arms: \(\overrightarrow{\mathrm{OA}}\); \(\overrightarrow{\mathrm{OB}}\)

Sides: \(\overrightarrow{\mathrm{OA}} ; \overrightarrow{\mathrm{OB}}\)

Vertex: O

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Sides And Vertex Of OC And OD Angles

Class 6 Math Solutions WBBSE

2. Arms: \(\overrightarrow{\mathrm{OC}}, \overrightarrow{\mathrm{OD}}\)

Sides: \(\overrightarrow{O C}, \overrightarrow{O D}\)

Vertex: O

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Sides And Vertex Of XY And YZ Angles

3. Arms: \(\overrightarrow{X Y}, \overrightarrow{Y Z}\)

Sides: \(\overrightarrow{X Y}, \overrightarrow{Y Z}\)

Vertex: Q

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Sides And Vertex Of PQ And QR Angles

4. Arms: \(\overrightarrow{P Q}, \overrightarrow{Q R}\)

Class 6 Math Solutions WBBSE

Sides: \(\overrightarrow{\mathrm{PQ}}, \overrightarrow{\mathrm{QR}}\)

Vertex: Y

Question 9. Let us draw the following angles with a protractor. Let’s name the angle and write their sides and vertex. Also mention the type of the angles – 38°, 75°, 90°, 145°, 180°, 200°, 270°.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles ABC Is 38 Degrees Acute Angle

1. ∠ABC =38°(Acute angle)

Sides: \(\overline{\mathrm{AB}}, \overline{\mathrm{BC}}\)

Vertex: B

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles PQR Is 75 Degrees Acute Angle

Class 6 Math Solutions WBBSE

2. ∠PQR = 75°(Acute angle)

Sides: \(\overline{\mathrm{PQ}}, \overline{\mathrm{QR}}\)

Vertex: Q

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles DEF Is 90 Degrees Rigth Angle

3. ∠DEF = 90°(Rigth angle)

Sides: \(\overline{\mathrm{DE}}, \overline{\mathrm{EF}}\)

Vertex: E

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles MNR Is 145 Degrees Obtuse Angle

4. ∠MNR = 145°(Obtuse angle)

Sides: \(\overline{\mathrm{MN}}, \overline{\mathrm{NR}}\)

Vertex: N

WBBSE Class 6 Maths Solutions

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles COD Is 180 Degrees Straigth Angle

5. ∠COD = 180°(Strigth angle)

Sides: \(\overline{\mathrm{CO}} ; \overline{\mathrm{OD}}\)

Vertex: O

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles IJK Is 200 Degrees Reflex Angle

6. ∠IJK = 200°, (Reflex angle)

Sides: \(\overline{\mathrm{IJ}}, \overline{\mathrm{JK}}\)

WBBSE Class 6 Maths Solutions

Vertex: J

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles APC Is 270 Degrees Reflex Angle

7. ∠APC = 270°(Reflex angle)

Sides: \(\overline{\mathrm{AP}}, \overline{\mathrm{PC}}\)

Vertex: P

Question 10. Let Do It
Solution:

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angle ABCD

∠BAD = 30°; ∠CAD = 60° and ∠BAC = 90°

∠BAD + ∠CAD = ∠BAC

Again, ∠BAC-∠BAD =∠DAC

∠ADC + ∠ADB = 180° = ∠BDC

∠BDC – ∠ADB = ∠ADC = 90°

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles

  1. ∠EAG + ∠GAF = 90°;
  2. ∠FAE – ∠FAG = 40°
  3. ∠ADC+ ∠ADB = 180°;
  4. 180°-∠ADC = 60°
  5. ∠SPR + ∠RPQ = ∠SPQ
  6. ∠SPQ – ∠SPR = ∠RPQ

Class 6 Math WBBSE Solutions Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Exercise 17.2

Question 1. Using the outer and inner scales of the protractor, let’s draw the following angles

1. 54°
Solution: Angle POQ = 54°

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles POQ Is 50 Degrees

2. 67°
Solution: ∠CDE = 67°

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles CDE Is 67 Degrees

3. 85°
Solution: ∠ABC = 85

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles ABC Is 85 Degrees

4. 95°
Solution: ∠MNK = 95°

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles MNK Is 95 Degrees

5. 120°
Solution: ∠RPK = 120°

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles RPK Is 120 Degrees

Class 6 Math WBBSE Solutions

Question 2. Let’s draw 187°, 235°, 310° and 325° angles using protractor:
Solution: 187°

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles ABC Is 187 Degrees

Reflex ∠ABC = 187°

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles PQR Is 235 Degrees

Reflex ∠PQR = 235°

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles PQR Is 235 Degrees

Class 6 Math WBBSE Solutions

Reflex ∠MKL = 310

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angles CDE Is 325 Degrees

Reflex ∠CDE = 325°

Question 3. Let’s observe the figure and comprehend and write:

  1. Let’s measure angle number 1, name the angle, type of angle. [Measure with protractor]
  2. Let angle number 2 be measured with a protractor, name the angle, and write the type of angle.
  3. The measures of angles 1 and 2 are added and the angle formed.

Solution:

1. ∠1 =40° (Acute angle)

∠BOC= 40°

2. ∠2 = 50° (Acute angle)

∠AOB = 50°

3. ∠1 + ∠2 = 40° + 50° = 90° (Right angle)

∠AOC = 90°

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angle ABC

Class 6 Maths Solutions WBBSE

Question 4. In the figure, let’s take angle number 1 = ∠AOB; angle number 2 = ∠BOC; angle number 3 = ∠COD

  1. Let’s measure angle number 1 with a protractor and note its value.
  2. Let’s measure angle number 2 with a protractor and note its value.
  3. Let’s measure angle number 3 with a protractor and note its value.
  4. By adding angle number 1 and angle number 2, we get an angle, name that angle from the figure. ‘
  5. By adding angle number 2 and angle number 3, the angle that is formed is named from the figure.
  6. The angle formed by adding angle number 1, number 2, and number 3 is named from the figure and let’s express it as the sum of three angles.

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Sum Of Thre Angles

Solution:

  1. ∠1 = ∠AOB = 60°
  2. ∠2 = ∠BOC = 90°
  3. ∠3 =∠COD = 30°
  4. ∠1 + ∠2 = ∠AOB + ∠BOC = 60° + 90° = 150°
  5. ∠2+ ∠3 = ∠BOC + ∠COD.= 90° + 30° = 120°
  6. ∠1 + ∠2 + ∠3 = ∠AOB+ ∠BOC+ ∠COD= 60° + 90° + 30° = 180°

Question 5. Let’s answer from the figure:

  1. Let’s name one acute angle: ∠AOB
  2. Let’s name one obtuse angle:∠BOD
  3. Let’s name one right angle: ∠COD
  4. Let’s name one straight angle: ∠AOD
  5. Let’s name a reflex angle: ∠AOE
  6. ∠AOB + ∠BOC =∠AOC
  7. ∠BOC + ∠COD = ∠BOD
  8. ∠AOC – ∠BOC = ∠AOB
  9. ∠BOD – ∠BOC = ∠COD

Class 6 Maths Solutions WBBSE Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Exercise 17.3

Question 1. Lengths of the sides of triangles are given. Let’s identify the types, of triangles according to angles:

  1. 18 cm 18 cm 10 cm;
  2. 5.2 cm, 5.2 cm, 5.2 cm;
  3. 8 cm, 2 cm, 9 cm

Solution:

1. 18 cm, 18 cm, 10 cm: Here the lengths of two sides of a triangle are equal, then it is an isosodes, triangle.

2. 5.2 cm, 5.2 cm, 5.2 cm: Here the lengths of three sides of a triangle are equal, then it is an equilateral triangle.

3. 8 cm, 8 cm, 9 cm: Here the lengths of the three sides of a triangle are not equal, then it is a scalene triangle.

Question 2. The measures of the three angles of the triangles are given below. Let’s identify the types according to angles:

  1. 90°, 45°, 45°
  2. 90°, 30°, 60°
  3. 75°, 70°, 35°
  4. 60°, 60°, 60″
  5. 120°, 30°, 60°

Solution:

1. 90°, 45°, 45°: Here one angle of a triangle is 90° and the other two angles are equal. So it is a right-angled isosceles triangle.

2. 90°, 30°, 60°: Here one angle is 90°; so, it is a right-angled triangle.

3. 75°, 70°, 35°: Here three angles of a triangle are not equal so it is a scalono trianglo.

4. 60°, 60°, 60°: Here three angles of a triangle are equal; so, it is an equilateral triangle.

5. 120°, 30°, 60°: Here one angle is 120°, greater than 90°- it is an obtuse angle. So tho triangle is an obtuse, angled triangle.

Question 3. A, B, and C are non-collinear points. Let’s join A, B; B, C, and C, A, and try to find answers of the following.

  1. Let’s identify the geometric figure formed by joining the line segments.
  2. Let’s write the angle opposite to side BC.
  3. Let’s write the angle opposite to side AC.
  4. Let’s write the side opposite to ∠BAC.
  5. Let’s write the side opposite to ∠ACB.

Solution:

  1. It is a triangle.
  2. ∠BAC
  3. ∠ABC
  4. Side BC
  5. Side AB

Class 6 Maths Solutions WBBSE

Question 4. Let’s find if the statements given below are correct or not
Solution:

  1. Hypotenuse is the smallest side of a right-angled triangle.(x)
  2. One angle of a right-angled triangle is 90°. (√)
  3. There are at least two acute angles in a triangle. (√)
  4. Each equilateral triangle is called an isosceles triangle. (√)
  5. The sum of three angles of a triangle is 360°. (X)
  6. The right-angled triangle can never be an equilateral triangle.(√)
  7. The right-angled triangle can not be an isosceles triangle. (X)

Question 5. Let’s try to draw 120°, 135°, 150° angles using set squares.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Agles Uing Set Squares

∠ABC = 90° + 45° = 135°

To draw 120°

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angle 120 Degrees

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angle 135 Using Square Sale

∠ABC = 90°+ 60° = 150°

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box Angle 150 Degrees Using Square Scales

To draw 150°

∠ABC = 90°+ 60° = 150°

WBBSE Math Solutions Class 6 Question 6. Let’s write the observations in a tabular form.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 17 Geometrical Concepts Based On Different Instruments Of Geometry Box

Question 7. Let’s write a logical statement for the set of words given below.

1. Square, Rectangle, Parallelogram — are all quadrilateral.
Solution: Square, rectangle, parallelogram — all have 4 sides, so they are quadrilateral.

2. A rectangle is a special type of parallelogram.
Solution: A rectangle is a special type of parallelogram as opposite sides of the rectangle are equal and parallel.

3. Parallelogram is a special trapezium.
Solution: Parallelogram is a special type of trapezium as the its two sides are parallel.

4. Rhombus is a special type of parallelogram.
Solution: Rhombus is a special type of parallelogram as its opposite sides are equal and parallel.

Question 8. Let’s mark (√) and (X) the incorrect and correct statements respectively given below:

  1. A rectangular figure has all the sides equal. (X)
  2. Each angle of a square is a right angle. (√)
  3. Opposite sides of a parallelogram are parallel. (√)
  4. For any trapezium, all its sides are equal. (X)
  5. None of the angles of a rhombus are right angles. (√)

 

WBBSE Solutions For Class 6 Maths Chapter 16 Concept Of Directed Numbers And Number Line

Class 6 Math Solutions WBBSE Chapter 16 Concept Of Directed Numbers And Number Line  Exercise 16

Question 1. Let us draw a number line put the following numbers on the line and name them.

1. Name + 5;- 2, + 3;- 6, + 2,- 5 respectively as A, B, C, D, E, and F.
Solution: + 5;-2; + 3;-6; + 2;-5,

WBBSE Solutions For Class 6 Maths Chapter 16 Concept Of Directed Numbers And Number Line Number Line

name as A, B, C, D, E, F respectively.

2. Let’s measure how many units E is from B.
Solution: Measure of E from B is units.

3. How many units is A from B towards right?
Solution: Measure of A from B towards the right is 7 units.

4. How many units is D from E towards left?
Solution: Measure of D from E towards the left is 8 units.

5. How many units is D from F towards left ?
Solution: Measure of D from F towards left is 1 unit.

Read and Learn More WBBSE Solutions For Class 6 Maths

6. What is the relation between the numbers which are at A and F?
Solution: Relation between the numbers which are at A and F – Mutually opposite numbers.

7. What are the absolute values of the numbers of B and E?
Solution: Absotute values of the numbers of B and E = 2.

Class 6 Math Solutions WBBSE

Question 2. What do the following mean?

1. Profit of -10 rupees
Solution: Profit of -10 rupees = Loss of Rs. 10.

2. -15 m above
Solution: -15 m above = 15 m down

3. -36 g less
Solution: -36 gm less = 36 gm more.

4. -18 meter towards East
Solution: -18 meter towards East = 18 meter toward West.

5. Saved -23 rupees
Solution: Saved -23 rupees = Spent Rs. 23.

6. -5 km towards South.
Solution: -5 km towards south = 5 km towards North.

Question 3. Let’s write the absolute values of the following numbers

  1. -12
  2. + 13
  3. – 22
  4. – 61
  5. + 17

Solution: Absolute value of the following

  1. -12 → 12
  2. +13 → 13
  3. -22 → 22
  4. -61 → 61
  5. +17 → 17

Class 6 Math Solutions WBBSE

Question 4. Let’s find the opposite of the following:

1. Spent Rs.-10
Solution: Spent Rs. -10 Rs. 10 saved

2. Climbed up -15 m.
Solution: Climbed up -15m 15m going up

3. Profit of 81
Solution: Profit of 81 :- Loss of Rs. – 81

4. move – 35m down
Solution: move – 35 m down: and 35 m up

5. – 24 kg increase in weight.
Solution: – 24 kg increase in weight = 24 kg weight decreased

6. 28 m towards the right
Solution: 28 m towards right = 28 m towards right

7. 9 kg decrease of weight.
Solution: 9 kg decrease of weight = 9 kg decrease of weight.

Question 5. Using a number line, put < or > in the blank spaces.

Class 6 Math Solutions WBBSE

1. 0 ______ 5
Solution: 0 < 5

2. 0 ________ -6
Solution: 0 > -6

3. 6 ________ -6
Solution: 6 > -6

4. – 8
Solution: -8 > -10

5. -1 ______ -11
Solution: -1 > -11

6. ______ 15
Solution: 11 < 15

7. —10 _____ 12
Solution: -10 < 2

8. -100 _____ -50
Solution: -100 < -50

Question 6. (1) Let’s write 4 negative whole numbers less than -12.
Solution: —15; —18; — 20; – 25;

(2) Let’s write 4 negative whole numbers greater than – 8.
Solution: -6; -4; -3; -1

Class 6 WBBSE Math Solutions Chapter 16 Concept Of Directed Numbers And Number Line  Exercise 16.1

Question 1. Let us add on a number line

1. (+7) – (+2)
Solution: (+7) – (+2)

WBBSE Solutions For Class 6 Maths Chapter 16 Concept Of Directed Numbers And Number Line Number Line 7-(+2)

∴ (+7) + (+2) = +9.

2. (+2)- (-4)
Solution: (+2)- (-4)

WBBSE Solutions For Class 6 Maths Chapter 16 Concept Of Directed Numbers And Number Line Number Line 2-(-4)

∴ (+2) + (—4) = -2

3. (+6) + (-11)
Solution: (+6) + (-11)

WBBSE Solutions For Class 6 Maths Chapter 16 Concept Of Directed Numbers And Number Line Number Line 6 And -11

∴ (+6) + (-11) = -5

Class 6 WBBSE Math Solutions

4. (-5), (-7)
Solution: (-5), (-7)

WBBSE Solutions For Class 6 Maths Chapter 16 Concept Of Directed Numbers And Number Line Number Line 5 And -7

∴ (-5), (-7) = -12

5. (+8) + (-8)
Solution: (+ 8), (-8)

WBBSE Solutions For Class 6 Maths Chapter 16 Concept Of Directed Numbers And Number Line Number Line 8 And -8

∴ (+8) + (-8) = 0

6. (+7), (-7)
Solution: (+7), (-7)

WBBSE Solutions For Class 6 Maths Chapter 16 Concept Of Directed Numbers And Number Line Number Line 7 And -7

∴ (+ 7) + (-7) = 0

7. (+9), (-17)
Solution: (+9), (-17)

WBBSE Solutions For Class 6 Maths Chapter 16 Concept Of Directed Numbers And Number Line Number Line 9 And -17

∴ + 9 +(-17)=-8.

Class 6 Maths Solutions WBBSE

8. (-11), (-9)
Solution: (-11), (-9)

WBBSE Solutions For Class 6 Maths Chapter 16 Concept Of Directed Numbers And Number Line Number Line -11 And -9

∴ (-11) +(-9) = -20

Question 2. Let’s add the following

1. (+9) + (+2)
Solution:

WBBSE Solutions For Class 6 Maths Chapter 16 Concept Of Directed Numbers And Number Line Number Line 9 + 2

(+9) + (+2) = + 11

2. (+11) – (+ 5)
Solution: (+11) +(+5) = +16

3. (+27) + (-11)
Solution: (+27)+ (-11) = +16

4. (-25) + (+6)
Solution: (-25) + (+6) = -19;

5. (-5) + (+9)
Solution: (—5) + (+9) = +4

6. (+13)+ (-13)
Solution: (+13) + (-13) = 0

Question 3. Let us simplify

1. (+13) + (+12) + (-10)
Solution: (+13) + (+12) + (-10) = +25 – 10 = (+15)

2. (+31) + (+13) + (-16)
Solution: (+31)+ (+13)+ (-16)

= +44 + (-16)

= 44 – 16 = (+28)

Class 6 Maths Solutions WBBSE

3. (+25) + (-16) + (+ 2)
Solution: (+25) +(-16) +(+2)

= (+9) + (+2)

= (+11)

4. (-11) + (+18) + (-16)
Solution: (-11)+ (+18)+ (-16)

= (+7)+ (-16)

= (-9)

Question 4. Let’s add the following

1. (-2), (-10), (+21)
Solution: (-2)+ (-10)+ (+21)

= (-12) + (+21)

= (+9)

2. (-18), (-7), (-2)
Solution: (-18) + (-7) + (-2)

=(-25)+ (-2)

= (-27)

Class 6 Maths Solutions WBBSE

3. (+10), (-8), (-10)
Solution: (+10) + (-8) + (-10)

= (+2) + (-10)

= (-8)

4. (-8), (-10), (+2)
Solution: (-8) + (-10) + (+2)

= (-18) + (+2)

= (-16)

5. (-19),(-9),(+5)
Solution: (-19) + (-9) + (+5)

= (-28) + (+5)

= (-23)

6. (+20), (-9), (-6)
Solution: (+ 20) + (-9) + (-6)

= (+11) + (-6)

= (+5)

7. (-14), (-12), (+ 21)
Solution: (-14) + (-12) + (+21)

= (-26) + (+21)

= (-5)

8. (-13), (+7), (-2)
Solution: (-13) + (+7) + (-2)

= (-6) + (-2)

= (-8)

9. (+15), (-9), (-5)
Solution: (+15) + (-9) + (-6)

= (+6) + (-6)

= 0

WBBSE Math Solutions Class 6 Chapter 16 Concept Of Directed Numbers And Number Line  Exercise 16.2

Question 1. Let’s do it

1. (- 6) – (+2) = _____
Solution: (-6) – (+2)

= -6-2 = —8

2. (-12) — (+12) = ______
Solution: (-12) – (+12)

= -12-12 = -24

3. (+11)-(+3) = ______
Solution: (+11)-(+3)

= 11-3 = +8

4. (-7) – (+8) = _____
Solution: (-7) – (+8)

= -7-8 = -15

5. (+20) – (-7) = ______
Solution: (+20) – (-7)

= 20 + 7 = 27

6. (-18)-(-8) = _________
Solution: (-18)-(-8)

= -18 + 8

= -10

7. (- 9) – (-9) = _______
Solution: (- 9) – (- 9)

= -9+9

= 0

WBBSE Math Solutions Class 6

8. (+ 13)- (-7) = ________
Solution: (+ 13)-(-7)

= 13 + 7 = 20

Question 2. Let’s complete the table given below

WBBSE Solutions For Class 6 Maths Chapter 16 Concept Of Directed Numbers And Number Line Equations

Solution:

WBBSE Solutions For Class 6 Maths Chapter 16 Concept Of Directed Numbers And Number Line Equations 1

Question 3. Let us mark (√) for the correct statement and (x) for wrong statement:

1. There are definite numbers of positive whole numbers.
Solution: There are definite numbers of positive whole numbers. [√]

2. 5.3 is a natural number.
Solution: 5.3 is a natural number. [X]

3. – 2.1 is a negative whole number.
Solution: -2.1 is a negative whole number. [x]

4. There is no existence of biggest whole number.
Solution: There is no existence of biggest whole number. [√]

WBBSE Math Solutions Class 6

Question 4. 1. (+14) — (+16)
Solution: (+14)-(+16)

= (+14)+ (-16)

= 14-16 = – 2

2. (+25) – (+21)
Solution: (+ 25)-(+21)

= (+ 25) + (-21)

= 25-21 = 4

3. (+ 34) – (-19)
Solution: (+ 34) – (-19)

= (+34)+ (+19)

= 34 + 19

= +53

4. (-15)-(-27)
Solution: (-15)-(-27)

=(-15)+(+27)

= -15 + 27

= +12

5. (-25) -(+13)
Solution: (-25) -(+13)

= (-25) + (-13)

= -25-13

= -38

6. (-16)-(-10)
Solution: (-16)-(-10)

= (-16)+ (+10)

= -16 + 10

= – 6

7. (+ 31) — (— 12)
Solution: (+31)-(-12)

= (+31)+ (+12)

= +31+12 = +43

8. (—31) — (—45)
Solution: (-31)-(-45)

= (-31)+ (+45)

= – 31 + 45 = +14

9. (-21)-(+21)
Solution: (-21)-(+21)

= (-21)+ (-21)

= -21-21

= -42

WBBSE Math Solutions Class 6

Question 5. Let’s put >, < or = in respective blank spaces:

1. (+13) + (- 8) _______ (+3) – (-2)
Solution: L.H.S. = (+13) + (-8)

= 13-8 = 5

R.H.S. = (+ 3) – (-2)

= 3 + 2 = 5

∴ (+13) + (-8) [ = ] (+3) – (-2)

2. (-12)-(-10) _______ (-9) +(+3)
Solution: L.H.S. = (-12)-(-10)

= -12 + 10 = – 2

R.H.S. = (-9) + (+3)

= -9 + 3

= -6

∴ (-12) – (-10) [ > ] (-9) + (+3)

3. (+35) – (-5) _____ (- 24) – (-64)
Solution: L.H.S. = (+ 35) – (-5)

= 35 + 5 = 40

R.H.S. = (-24)-(-64)

= – 24 + 64 = 40

∴ (+35) – ( -5) [ = ] (-24) – (-64)

Class 6 Math WBBSE Solutions

4. (-18) – (+6) ______ (-18) – (-6)
Solution: L.H.S. = (-18) – (+6)

= -18-6 = -24

R.H.S. = (-18) -(-6)

= -18 + 6 = -12

∴ (-18) (+ 6) [ < ] (—18) — (—6)

5. (-45) – (-52) _______ (-52) – (-45)
Solution: L.H.S. = (-45) – (-52)

= -45 + 52 = + 7

R.H.S. = (-52)-(- 45)

= – 52 + 45 = —7

∴ (-45) – (—52) [ > ] (-52) – (-45)

6. (+25) -(-19) _______ (-25) -(+19)
Solution: L.H.S. = (+25)-(-19)

= +25 + 19 = + 44

R.H.S. = (-25)-(+19)

= -25-19 = -44

∴ (+25) — (—19) [ > ] (—25) – (+19)

Question 6. Let’s put number in blank spaces:

1. (-3) + ________ = 0
Solution: (—3) + [+3] = 0

2. (+16) + ________ = 0
Solution: (+16) + [-16] = 0

3. (-9) + _______ = (-15)
Solution: (-9) + [-6] = – 15

4. _____ + (-7) = (-10)
Solution: [-3] +(-7) = (-10)

Question 7. Let’s simplify:

1. (-5) + (opposite number of -7) – (-5)
Solution: (-5) + (+7) + (5)

= + 7

2. 12 – (-3) + (opposite number of +6)
Solution: 12 + 3 + (-6)

= 15-6 = 9

3. 15 – (+4) + (opposite number of +9)
Solution: 15 – 4 + (-9)

= 15-4-9 = 15-13 = 2

4. (opposite number of +20) – (opposite number of -7) – (-8)
Solution: (-20) – (+7) + 8

= -20 – 7 + 8 = – 27 + 8

= -19

Question 8. Let’s find what must be added to the first to get the second:

1. -7,-12
Solution: -12-(-7)

= -12 + 7 = – 5

2. 24, – 32
Solution: -32 – (+24)

= – 32 – 24

= -56

3. -17,12
Solution: 12-(-17)

= 12+17

= 29

Class 6 Math WBBSE Solutions

4. 16, 0
Solution: 0 – (+ 16)

= 0-16

= -16

5. 25,-42
Solution: -42 – (+25)

= -42 -25 = -67

Question 9. Let’s find what must be added to the first to get the second:

1. (+7), (+2)
Solution: (+2) – (+7)

= 2-7 = -5

.2. (+7), (-2)
Solution: (-2)-(+7)

= -2-7 = —9

3. (-7), (+2)
Solution: (+2)-(-7)

= 2 + 7 = 9

4. (-7), (-2)
Solution: (-2)-(-7)

= -2 + 7

= + 5

Question 10. Let’s verify the commutative property of addition for the following:

1. (+5), (+3)
Solution: (+5) + (+3) = +8,

Again, (+3) + (+5) = +8 (+5) + (+3) = (+3) + (+5)

2. (+ 5), (-3)
Solution: (+5) + (-3) = +2,

Again, (-3) + (+5) = + 2 (+5) + (-3) = (-3) + (+5)

3. (-5), (+3)
Solution: (-5) + (+3) = -2,

Again, (+3) + (-5) = – 2 (-5) + (+3) = (+3) + (-5)

4. (-5), (-3)
Solution:

(-5) + (-3) = -8,

Again (-3) + (-5) = -8

(-5) + (-3) = (-3) + (-5)

Question 11. Let’s verify the associative property of addition for the following:

1. (+5), (+3), (+2)
Solution: (+5), (+3), (+2)

= {(+5) + (+3)} + (+2)

= (+8) + (+2)

= (+10)

and, = (+5) + {(+3) + (+2)}

= +5 + 5 = (+10)

{(+5) + (+3)} + (+2)

= (+5) + {(+3) + (+2)}

2. (+5), (-3), (+2)
Solution: (+5), (-3), (+2)

= {(+5) + (-3)) + (+2)

= (+2) + (+2) = (+4)

and, (+5) + {(-3) + (+2)}

= (+5) + (-1) = (+4)

= {(+ 5) + (-3)} + (+2)

= (+5) + {(-3) + (+2)}

Class 6 Math WBBSE Solutions

3. (-5), (-3), (+2)
Solution: (-5), (-3), (+2)

{(-5) + (-3)} + (+2)

= (-8) + (+2) = -6 and, (—5) + {(—3) + (+2)}

= (—5) + (—1) = -6

{(-5) + (-3)} + (+2)

= -5 + {(-3) + (+2)}

4. (—5), (—3), (-2)
Solution: (-5), (-3), (-2)

{(- 5) + (-3)} + (-2)

= (-8) + (-2) = (-10)

and, (-5) + {(-3) + (-2)}

= (- 5) + (- 5) = (-10)

{(-5) + (-3)} + (-2)

= (-5) + {(-3) + (-2)}

 

WBBSE Solutions For Class 6 Maths Chapter 15 Determination Of Area And Perimeter

Class 6 Math Solutions WBBSE Chapter 15 Determination Of Area And Perimeter Exercise 15

Let’s us draw, observe and write what I know

Question 1. I found my brother’s first geometric shape model is a triangle.
Solution:

Its perimeter is = _____ cm + _______ cm + ______ cm = 3 x 12 cm

To put a border around this geometric model, we need 36 cm of colored paper.

WBBSE Solutions For Class 6 Maths Chapter 15 Determination Of Area And Perimeter 1st Geometric Shape Model Is An Triangle

Solution:

Perimeter of the 1 st figure = 12 cm + 12 cm + 12 cm = 36 cm

Question 2. Let me find the perimeter of the second geometric figure. The perimeter of the second geometric figure = _____ cm + ________ cm + _________ cm + _________ cm = _______ cm. I shall need ______ cm of colored paper to put a border on it.

WBBSE Solutions For Class 6 Maths Chapter 15 Determination Of Area And Perimeter Second Geometric Figure

Solutions:

Perimeter of the 2nd figure

= 20 cm + 22 cm + 22 cm + 18 cm = 82 cm

Read and Learn More WBBSE Solutions For Class 6 Maths

Question 3. The perimeter of the third geometric shape is = ________ cm + _______ cm + _____ cm + ______ cm + ________ cm + _____ cm = ________ cm

WBBSE Solutions For Class 6 Maths Chapter 15 Determination Of Area And Perimeter Third Geometric Shape

Solution:

Perimeter of the 3rd figure = 6 cm + 6 cm + 6 cm + 6 cm + 6 cm + 6 cm = 36 cm

Class 6 Math Solutions WBBSE

Question 4. Perimeter of the fourth geometric figure. = _____ cm + _____ cm + ______ cm + ______ cm + ______ cm + _______ cm + _______ cm + ______ cm + = _____ cm

WBBSE Solutions For Class 6 Maths Chapter 15 Determination Of Area And Perimeter Perimeter Of The Fourh Geometric

Solution:

Perimeter of the 4th figure

= 5 cm + 13 cm + 30 cm + 13 cm + 5 cm + 7 cm + 20 cm + 7 cm

= 100 cm

Question 5. Perimeter of fifth geometric figure = _____ cm. + _______ cm + _____ cm + ________ cm + ______ cm + _________ cm + _______ cm + _______ cm = _____ cm

WBBSE Solutions For Class 6 Maths Chapter 15 Determination Of Area And Perimeter Perimeter Fifth Geometric

Solution:

Perimeter of the 5th figure

= 16 cm + 4 cm + 6 cm + 10 cm + 4 cm + 10 cm + 6 cm + 4 cm = 60 cm

WBBSE Math Solutions Class 6

Question 6. Let’s find the perimeter of the sixth geometric figure.

WBBSE Solutions For Class 6 Maths Chapter 15 Determination Of Area And Perimeter Perimeter Of Sixth Geometric

Solution:

Perimeter of the 6th figure

= 4 cm + 9 cm + 11 cm + 9 cm + 4 cm + 22 cm + 4 cm + 9 cm + 11 cm + 9 cm + 4 cm + 22 cm = 118 cm.

Hands-on trial: Now, we shall join points on graph paper to form different geometric figures and try to find the space occupied by these figures.

We pasted the graph paper on a cardboard. We formed different geometric figures on it by joining points and let’s try to find the area enclosed by them.

WBBSE Solutions For Class 6 Maths Chapter 15 Determination Of Area And Perimeter Graph Paper To Form Different Geometric Figures

Example: Let’s fill up the data and let’s measure the area:
Solution:

WBBSE Solutions For Class 6 Maths Chapter 15 Determination Of Area And Perimeter Data With Measure Area

 

WBBSE Solutions For Class 6 Maths Chapter 14 Concept Of Line Segment Ray And Point

Class 6 Math Solutions WBBSE Chapter 14 Concept Of Line Segment Ray And Point

Let’s us draw, observe, and write what I know

My friends and me draw pictures, observe and identify the things we know, let’s note down

WBBSE Solutions For Class 6 Maths Chapter 14 Concept Of Line Segment Ray And Point Cottage And House

Example 1. Figure (1) is the picture of a ____.
Answer:

Figure (1) is a picture of a cottage or house.

Example 2. In the picture of the house we can find many ___ [Straight lines or Angular points]
Answer:

In the picture of the house we can find many Angular points.

Read and Learn More WBBSE Solutions For Class 6 Maths

Example 3. Let’s mention the four angular points — ______, ____, _____, ______ and mark them with ‘O’ in the picture.
Answer:

The four angular points are A, B, C, and D.

Example 4. Again, we find several ____[Ray/Line segment] in the picture of the house. From Figure (1) let us find and name 4 of the line segments ____, ___, _____, and _____
Answer:

Again, we find several line segments in the picture of the house. From Figure (1) 4 names of the line segments are AB, BC, CD, and GD.

Example 5. We find the line segments DE and DC are intersecting at ______.
Answer:

We find the line segments DE and DC intersect at D.

Class 6 Math Solutions WBBSE

Example 6. Again, in Figure (1) ______ and ____ line segments have intersected at E.
Answer:

Again, in Figure (1) DE and EF line segments have intersected at E

Example 7. But, we see the 2 line segments DE, CF, and the line segments DC and _____ are on the same plane but they will never intersect each other, no matter how far they be produced on either side.
Answer:

But, we see the 2 line segments DE, CF, and the line segments DC and EF are on the same plane but they will never intersect each other, no matter how far they be produced on either side.

Example 8. The line segments DE and DC are on the same plane and intersect each other at ____, hence these lines are called _____(Intersecting/Parallel).
Answer:

The line segments DE and DC are on the same plane and are intersecting each other at D, hence these lines are called Intersecting.

Example 9. The line segments DE and CF are on the same plane but will never meet, no matter how far they be produced. Hence, these line segments are (Intersecting/Parallel).
Answer:

The line segments DE and CF are on the same plane but will never meet, no metter how far they are produced. Flence these line segments are parallel.

Class 6 WBBSE Math Solutions Chapter 14 Concept Of Line Segment Ray And Point Exercise 14

Question 1. From the picture (2), let’s identify 4 angular points and name them _______, _________, ________, ______
Solution:

From the picture (2), let’s identify 4 angular points and name them I, J, K, L.

Question 2. Let’s identify and write the four line segments which are named in the picture (2) _______, ______ and ______
Solution:

Let’s identify and write the four line segments which are named in the picture (2) SP, PQ, QR, and SR.

Question 3. From picture (2), let’s identify two pairs of intersecting line segments on a plane and find the points at which they intersect.
Solution:

  1. SP, PQ are two pairs of intersecting line segments at P as intersecting point.
  2. SP, SR are two pairs of intersecting line segments at S as an intersecting point.
  3. SR, QR are two pairs of intersecting line segments at R as an intersecting point.
  4. QR, PQ are two pairs of intersecting line segments at Q as an intersecting point.

Question 4. In picture (2), let’s find two pairs of parallel line segments on a plane which are already named in the figure.
Solution:

PQ || SR and SP || QR are two pairs of parallel line segments on a plane.

Question 5. From the picture (3) — let’s identify and write 3 intersecting points and 4 line segments already named in the picture.
Solution:

3 intersecting points: M, N, O.

4 line segments: MN; NO; OP and PM.

Class 6 Maths Solutions WBBSE Chapter 14 Concept Of Line Segment Ray And Point 14.1

Question 1. Let’s draw 6 concurrent straight lines and name them.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 14 Concept Of Line Segment Ray And Point 6 Concurrent Straight Lines

The 6 concurrent straight lines are \(\overrightarrow{A B}, \overrightarrow{C D}, \overrightarrow{E F}, \overrightarrow{G H}, \overrightarrow{I J}, \ \overrightarrow{K L}\)

Question 2. 5 non-collinear points are to be drawn and find how many straight lines can be drawn through them.
Solution:

A, B, D, and E, are 5 non-collinear points

WBBSE Solutions For Class 6 Maths Chapter 14 Concept Of Line Segment Ray And Point 5 Non Collinear Points

Through the point A, we can draw 4 straight lines.

Through the point B, we can draw 3 straight lines.

Through the point C, we can draw 2 straight lines.

Through the point D, we can draw 1 straight line

Question 3. Let’s draw 5 points which are collinear.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 14 Concept Of Line Segment Ray And Point 5 Collinear Points

The points A, B, C, D, and E are 5 collinear points.

WBBSE Math Solutions Class 6 Chapter 14 Concept Of Line Segment Ray And Point 14.2

Question 1. Let’s identify the points of intersection in the following figures and note them down.

WBBSE Solutions For Class 6 Maths Chapter 14 Concept Of Line Segment Ray And Point Intersection Of Following Figures

Solution:

  1. D, E, and F are the points of intersection.
  2. P, Q, R, S, and T are the points of intersection.
  3. A, B, C, and D are the points of intersection.
  4. K, L, M, N, and O are the points of intersection.

Question 2. In the figures given below, let’s identify line segments and rays and note them down.

WBBSE Solutions For Class 6 Maths Chapter 14 Concept Of Line Segment Ray And Point Line Segments And rays

Solution:

1. Line segments = \(\overline{X Y}, \overline{X Z}\)

Rays = \(\overrightarrow{X Y}, \overrightarrow{X Z}\)

2. Line segments = \(\overline{\mathrm{AD}}, \overline{\mathrm{AB}}, \overline{\mathrm{BC}}\)

Rays = \(\overrightarrow{A D}, \overrightarrow{B C}\)

3. Line segments = \(\overline{\mathrm{AB}}, \overline{\mathrm{BC}}, \overline{\mathrm{CD}}, \overline{\mathrm{DE}}\)

Rays = \(\overrightarrow{B A}, \overrightarrow{D E}\)

4. Line segments = \(\overline{\mathrm{AB}}, \overline{\mathrm{CD}}\)

Rays = \(\overrightarrow{O B}, \overrightarrow{O C}\)

Question 3.

WBBSE Solutions For Class 6 Maths Chapter 14 Concept Of Line Segment Ray And Point Collinear Points

  1. What are these three points X, Y, and Z called?
  2. How many line segments are formed with these three points?

Solution:

The points X, Y, and Z are called collinear points.

Three line segments are formed with these points.

WBBSE Math Solutions Class 6

Question 4. From the figure:

  1. Let’s find and write three pairs of parallel lines.
  2. Let us find and write three pairs of intersecting lines.
  3. Let us find and write six-line segments.

WBBSE Solutions For Class 6 Maths Chapter 14 Concept Of Line Segment Ray And Point Six Line Segments

Solution:

1. \((\stackrel{\leftrightarrow}{A B}, \overleftrightarrow{C D}),(\overleftrightarrow{C D}, \overleftrightarrow{E F}),(\stackrel{\leftrightarrow}{A B}, \overleftrightarrow{E F})\)

2. \((\stackrel{\leftrightarrow}{\mathrm{PQ}}, \stackrel{\leftrightarrow}{\mathrm{MN}}) ;(\stackrel{\leftrightarrow}{\mathrm{PQ}}, \overleftrightarrow{\mathrm{G}-1}) \&(\stackrel{\leftrightarrow}{\mathrm{MN}}, \stackrel{\leftrightarrow}{\mathrm{RS}})\)

3. \((\overline{\mathrm{PB}}, \overline{\mathrm{AC}}, \overline{\mathrm{CE}}, \overline{\mathrm{BD}}, \overline{\mathrm{DF}}, \& \overline{\mathrm{AB}})\)

Question 5. From the figure:

  1. Let’s find the points of intersection.
  2. Let’s write all sets of collinear points separately.
  3. Let’s write the line segments separately.
  4. Let’s write the line segments that are concurrent.

WBBSE Solutions For Class 6 Maths Chapter 14 Concept Of Line Segment Ray And Point Line Segments And Concurrent

Solution:

  1. A, F, B, D, C, E and 0.
  2. (A, F, B); (A, O, D), (A, E, C); (B, D, C); (C, 0, F), (B, O, E).
  3. AB, BC, CA, AF, FB, AB, AD, OD, BO, BE, OE, CO, CF, OF, AE EC BD DC
  4. AD, BE and CF.

Question 6. Let us put (√) for correct and (x) for wrong answers

WBBSE Solutions For Class 6 Maths Chapter 14 Concept Of Line Segment Ray And Point Line Segment

1. On the line segment \(\overrightarrow{\mathrm{YW}}\), Z and W are coliinear.

2. \(\overrightarrow{\mathrm{ZV}}\) and \(\overrightarrow{\mathrm{WV}}\) are the same rays.

3. \(\overrightarrow{\mathrm{ZV}}\) and \(\overrightarrow{\mathrm{ZX}}\) are same rays.

4. On the ray \(\overrightarrow{\mathrm{YX}}\), Z is a point.

WBBSE Math Solutions Class 6

Solution:

1. On the line segment \(\overrightarrow{\mathrm{YW}}\), Y, Z and W are coliinear. (√)

2. \(\overrightarrow{\mathrm{ZV}}\) and \(\overrightarrow{\mathrm{WC}}\), \(\overrightarrow{\mathrm{WV}}\) WV are the same rays- (√)

3. \(\overrightarrow{\mathrm{ZV}}\) and \(\overrightarrow{\mathrm{ZX}}\) are the same raYs- (X)

4. On the ray \(\overrightarrow{\mathrm{YX}}\), Z is a point. (X)

Question 7. Let’s try and find the answers

1. How many straight lines can be drawn through one fixed point?
Solution: Infinite

2. How many straight lines can be drawn through two fixed points?
Solution: One

3. How many line segments can be drawn through three non-collinear points?
Solution: Three

4. How many endpoints are there in a line segment \(\overline{\mathrm{AB}}\)?
Solution: A, B

5. How many endpoints are there in ray \(\overrightarrow{\mathrm{AB}}\)?
Solution: A, B

6. Straight line, line segment, and ray — of these three which one has a fixed length?
Solution: Line segment

7. Are the rays \(\overline{\mathrm{AB}}\) and \(\overline{\mathrm{BA}}\) same?
Solution: Not Same

8. Are the line segments \(\overrightarrow{\mathrm{AB}}\) and \(\overrightarrow{\mathrm{BA}}\) equal? In what way are they equal?
Solution: Yes

9. What is the maximum number of points at which two line segments can meet?
Solution: One

WBBSE Math Solutions Class 6

10. Let’s find the maximum number of points at which three non-concurrent lins can intersect.
Solution: Three

Question 8. Let’s draw ourselves

1. \(\overline{\mathrm{PQ}}\) and \(\overline{\mathrm{RS}}\) are two line segments interseceting at O.

2. Using scale, let us draw \(\stackrel{\leftrightarrow}{\mathrm{AB}}\) and \(\stackrel{\leftrightarrow}{\mathrm{CD}}\) as two Parallel lines

3. Let’s draw a ray \(\overrightarrow{\mathrm{MN}}\) on which S is a point.

4. Let’s draw two line segments AC and DC meeting at C.

Solution:

WBBSE Solutions For Class 6 Maths Chapter 14 Concept Of Line Segment Ray And Point Two Line Segments

  1. PQ and RS are two line segments interecting at O.
  2. AB and CD are two parallel line segments.
  3. MN is a ray on which S is a point.
  4. AC and CD are two line segments meeting at C.

Question 9. From the figure given below, let’s measure the lengths with scale and fill in the blank spaces accordingly.

WBBSE Solutions For Class 6 Maths Chapter 14 Concept Of Line Segment Ray And Point Length With Scale

1. \(\overline{\mathrm{PQ}}+\overline{\mathrm{QR}}\)=____ \(\mathrm{cm} \cdot=\overline{\mathrm{PR}}\)

2. \(\overline{\mathrm{QR}}+\overline{\mathrm{RS}}\) = _____ \(\mathrm{cm}\) = _____

3. \(\overline{\mathrm{PS}}\) = ____ + \(\overline{\mathrm{QR}}\) + _____

4. \(\overline{\mathrm{PR}}-\overline{\mathrm{QR}}\) = _______ cm = _______

5. PR – PQ = ______ cm

6. QS – QR = _______ cm.

7. QS – RS = ______ cm.

Solution:

WBBSE Solutions For Class 6 Maths Chapter 14 Concept Of Line Segment Ray And Point Length 3 With Scale

1. \(\overline{\mathrm{PQ}}+\overline{\mathrm{QR}}=(3+3) \mathrm{cm} \cdot=\overline{\mathrm{PR}}=6 \mathrm{~cm}\)

2. \(\overline{\mathrm{QR}}+\overline{\mathrm{RS}}=(3+3) \mathrm{cm} .=\overline{\mathrm{QS}}=6 \mathrm{~cm}\)

3. \(\overline{\mathrm{PS}}=\overline{\mathrm{PQ}}+\overline{\mathrm{QR}}+\overline{\mathrm{RS}}\)

4. \(\overline{\mathrm{PR}}-\overline{\mathrm{QR}}=3 \mathrm{~cm} .=\overline{\mathrm{PQ}}\)

5. \(\mathrm{PR}-\mathrm{PQ}=(6-3) \mathrm{cm}=3 \mathrm{~cm}\)

6. \(\mathrm{QS}-\mathrm{QR}=(6-3) \mathrm{cm}=3 \mathrm{~cm}\)

7. \(\mathrm{QS}-\mathrm{RS}=(6-3) \mathrm{cm}=3 \mathrm{~cm}\)

WBBSE Solutions For Class 6 Maths Chapter 13 Data Handling And Analysis

Class 6 Math Solutions WBBSE Chapter 13 Data Handling And Analysis Exercise 13

Example: Like every year, this year the Physical Education teacher of our school took measurements (in cm) of the height of the students of class 6 who would be taking part in school sports. The data obtained is given below

WBBSE Solutions For Class 6 Maths Chapter 13 Data Handling And Analysis Physical Education Teacher Measurments

The shortest height = 120 and the tallest height = 127.

WBBSE Solutions For Class 6 Maths Chapter 13 Data Handling And Analysis School Sports Number Of Students And Heigth

Question 1. In a class test of 15 marks, I prepare a list showing marks obtained by 20 students. Let’s write down these marks by giving tally marks and prepare a frequency distribution chart. 9, 8, 6, 10, 2, 1,15, 12, 8, 6, 9, 2, 8, 5, 9, 10, 5, 9, 10, 8
Solution:

Frequency Distribution Table

Read and Learn More WBBSE Solutions For Class 6 Maths

WBBSE Solutions For Class 6 Maths Chapter 13 Data Handling And Analysis Frequency Distribution Table Marks Obtained By 20 Students

Question 2. In Jahanara’s school classes were held for 22 days only this month. The number of students attending classes on these 22 days are given below. 30, 28, 34,29,25,30,28,26,29,30, 22,25,26,29, 30, 31,21,27, 25,13, 32, 28. Using the above raw data, let’s prepare a frequency distribution chart with tally marks.

Class 6 Math Solutions WBBSE
Solution:

Frequency distribution table

WBBSE Solutions For Class 6 Maths Chapter 13 Data Handling And Analysis Frequency Distribution Table Jahanara's School Classes For 22 Days Only This Month

Question 3. Given below is the data showing what fruits my 20 friends like to have. Let me draw a bar graph based on this data.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 13 Data Handling And Analysis Bar Graph For Number Of Friends And Number Of Fruits

Question 4. I prepared a raw data showing the number of students present in the class for 6 days of this week. From this raw data, I prepare a list using tally marks. Let’s write down from the list the day of week on which least number of students are present.
Solution:

I prepare a raw data showing number of students present in the class for 6 days of the week.

Class 6 Math Solutions WBBSE

WBBSE Solutions For Class 6 Maths Chapter 13 Data Handling And Analysis Number Of Days Number Of Students Present Table

Frequency distribution table

WBBSE Solutions For Class 6 Maths Chapter 13 Data Handling And Analysis Frequency Distribution Table Students Present In Class For 6 Days Of This Week

Question 5. I write down the weight (kg) of 30 students of class VI of Soham’s school. 32, 32, 37, 34, 37, 35, 35, 36,37, 39, 40, 36, 37, 36, 33,31,32,36, 37,38, 40, 34, 36, 34, 35, 33, 34, 35, 32, 35 Using the above raw data, let’s prepare a frequency distribution chart.
Solution:

Weight (kg) of 30 students of class 32, 32, 37, 34, 37, 35, 35, 36, 37, 39, 40, 36, 37, 36, 33, 31,32, 36, 37, 38, 40, 34, 36, 34, 35, 33, 34, 35, 32, 35

Frequency Distribution Table

Class 6 Math Solutions WBBSE

WBBSE Solutions For Class 6 Maths Chapter 13 Data Handling And Analysis Frequency Distribution Table Weigth Of 30 Students For Class 6

Question 6. From a survey conducted on 150 students of our school, it is seen how many students like to study a special subject. The raw data from the survey is given below
Solution:

WBBSE Solutions For Class 6 Maths Chapter 13 Data Handling And Analysis Survey Conducted On 150Students Of Our School

WBBSE Solutions For Class 6 Maths Chapter 13 Data Handling And Analysis Number Of Students And Number Of Subjects Bar Graph

Question 7. Ram da has a shop selling bags in Haidar Para. Ram da himself makes the bags. I prepare a list of bags sold from the shop this week.

WBBSE Solutions For Class 6 Maths Chapter 13 Data Handling And Analysis Number Of Bags Sold List

Let take a scale of my choice and draw a bar diagram.
Solution:

WBBSE Solutions For Class 6 Maths Chapter 13 Data Handling And Analysis Number Of Bags Sold And Number Of Days Bar Graph

Question 8. I have prepared a bar diagram showing the number of students appearing at the Madhymik Examination each year during the five years.

  1. I have prepared a set of questions from the bar diagram and let’s answer the questions.
  2. Let us see in which year a maximum number of students have sat for the exam.
  3. Let us see in which year least number of students have sat for the exam.
  4. Let see how many more students have appeared for the examination in 2011 than in 2010.
  5. In 2010, let us see how many less students have appeared for the exam than in 2009.
  6. Let’s see how many total students have sat for examination between 2008 and 2010.

Class 6 WBBSE Math Solutions

Solution:

WBBSE Solutions For Class 6 Maths Chapter 13 Data Handling And Analysis Number Of Candidats In A Year

  1. 2012
  2. 2010
  3. 120-100 = 20
  4. 100-90 = 10
  5. 110 + 100 + 90

 

WBCHSE Class 11 Chemistry Notes For Intermolecular Forces – Definition and Types

States Of Matter

That matter exists in three physical states—solid, liquid and gaseous—is something you know from everyday experience. You must also be aware of the fact that a particular substance can exist as a solid, a liquid, or a gas, depending upon the temperature and pressure, example, water can exist in all three states.

In fact almost all substances can exist in the three states if the conditions of pressure and temperature are appropriate. Also, every pure substance can exist in the three states simultaneously (the three states are said to be in equilibrium) at a characteristic temperature and pressure called the triple point, about which you will learn later.

Generally speaking, we call a substance a solid if its melting point is above room temperature, a liquid if its melting point is below room temperature and boiling point is above room temperature, and a gas if its boiling point is below room temperature. This is under atmospheric pressure.

Read and Learn More WBCHSE For Class11 Basic Chemistry Notes

  • Certain other differences in the properties or behaviour of solids, liquids and gases are obvious from common observation. A solid, for example, has a definite shape and volume. It cannot be compressed easily and generally has a high density.
  • A liquid has a definite volume but not a definite shape—it takes on the shape of the vessel it is poured into. It can be compressed more easily than a solid and generally has a lower density than a solid. A gas has neither a definite shape, nor a definite volume. It is highly compressible and has the least density among the three, i.e., solid, liquid and gas.
  • Tire differences in these macroscopic or bulk properties of the three states of matter are due to the different arrangements of the constituent particles in the different states.
  • In solids, the constituent particles are packed closely and are held together by a strong force of attraction between the particles. In liquids, the distance between the particles is greater and this force is weaker.
  • In gases, the particles are far apart and this force is negligible. The particles in a solid are not really free to move. They possess only vibratory motion. The particles in a liquid enjoy greater freedom of movement. The particles constituting a gas have the greatest freedom of movement.

WBCHSE Class 11 Chemistry Notes For Intermolecular Forces – Definition and Types

Intermolecular Forces

Intermolecular forces are responsible for the bulk properties of matter such as melting point and boiling point. The word bulk indicates a collection of atoms, molecules or ions. Intermolecular forces are those which exist between molecules as against intramolecular forces which hold the atoms together.

  • In order to understand the difference between the two types of forces, let us take the example of water whose chemical formula is H2O. There are two O—H bonds in the molecule and the energy required to break the two bonds is high; it is 930 kJ per mole of water.
  • However, if we want to evaporate water, it requires only 41 kJ per mole of water. Generally, intermolecular forces are weaker than intramolecular forces.What are the forces that hold together the molecules in the different states of matter?
    What are the physical laws that govern the formation of a particular state of matter?
    Let us now study the types of forces existing between the particles of a matter that make it acquire a particular state.
    The particles may be molecules, atoms or ions.

van der Waals forces: Dipole-dipole forces, dipole-induced dipole and dispersion forces make up van der Waals forces, called so after the Dutch physicist Johannes van der Waals. These occur between molecules (intermolecular forces) or atoms (interatomic forces).

Basic Chemistry Class 11 Chapter 5 States Of Matter Dipole-dipole Forces In Polar Molecules Attraction And Repulsive

Dipole-dipole forces Neutral but polar molecules experience dipole forces as a result of electrical interactions among dipoles on neighbouring molecules. There is partial positive (δ+) or partial negative (δ-) charge associated with the two ends of the dipoles in a molecule.

  • The molecules in a sample could be oriented in various ways and so the forces could be attractive (when unlike charges are close together) or repulsive (when like charges are close together) between the dipoles of neighbouring molecules.
  • The overall effect is the average of all such forces. The potential energy is lower for the attractive orientation and so this predominates. The net potential energy will, therefore, be an average of the different orientations.
  • It increases as the distance between the interacting dipoles decreases. The potential energy of interaction is proportional to 1/r6 where r is the distance between the dipoles (molecules). It also varies inversely as a function of temperature.

The strength of the given dipole-dipole interaction depends on the sizes of the dipole moments involved. The more polar the substance, the greater is the strength of its dipole-dipole interaction. This is reflected in the boiling point values for different substances. Substances with higher dipole moments tend to have higher boiling points.

Dipole-induced dipole forces Let us first understand what an induced dipole is. A molecule having a permanent dipole moment (polar molecule) can induce a dipole in another molecule by deforming its electronic cloud. The latter molecule, thus, gets an induced dipole.

  • This induced dipole interacts with the dipole of the other molecule and the forces involved are called dipole-induced dipole forces. The strength of the interaction depends on the dipole moment of the polar molecule and the polarisability (the ease with which the electron cloud can get deformed) of the second molecule.
  • The potential energy of interaction is directly proportional to these two factors. It also varies as 1/r6 as in the case of dipole-dipole forces.

Basic Chemistry Class 11 Chapter 5 States Of Matter Dipole Induced Dipole Forces Between Permanent And Induced Dipoles

London dispersion forces Intermolecular forces not only exist between charged and polar particles but also among nonpolar molecules. These are called London dispersion forces after Fritz London, who first explained them. In fact, all atoms and molecules experience London dispersion forces which result from the motion of electrons.

  • Let us consider the example of a nonpolar molecule Br2. It has a zero dipole moment averaged over time but at any point of time, the electrons may be more towards one end than the other resulting in a short-lived dipole. This dipole may induce temporary dipoles in neighbouring molecules resulting in attractive forces between the molecule with the permanent dipole and the neighbouring molecule.
  • These forces are weak and the energy of interaction is small, in the range of 1-10 kJ mol-1. The exact magnitude of the energy depends on the polarisability of the molecule. Smaller atoms or molecules are less polarisable as compared to larger ones and the dispersion forces are also loss. This can be easily understood by taking halogens as examples. F2 and Cl2 are gases at room temperature, Br2 is a liquid and I2 is a solid.

The intermolecular force of attraction increases in the order: F2 <Cl2; <Br2, <I2.

The increase in force of attraction with the increase in the size of atoms involved can be explained by London’s theory, In a larger atom, the valence electrons are, on an average, farther from the nuclei than those in a smaller atom.

  • Also, they are loss tightly held and can more easily form the temporary dipoles that cause the attraction between molecules. Dispersion forces usually increase with molar mass because such molecules have more electrons and dispersion forces increase in strength with the number of electrons. Another factor which is important in determining the magnitude of the dispersion forces is its shape.
  • Shapes which have larger molecular surface area allow greater contact between molecules and give rise to higher dispersion forces than do compact molecules. For instance, the boiling point of u-pentane is 309.4 K while that of neopentane or 2,2-dimethyl propane is 282.7 K though both of them have the same molecular formula.
  • Tire reason behind this behaviour is that in n-pentane there is a possibility of greater contact between molecules because of its spread-out structure. Hence, this leads to stronger intermolecular dispersion forces and, therefore, a higher boiling point.
  • The potential energy associated with London dispersion forces is again inversely proportional to the sixth power of the distance between tire molecules.

Basic Chemistry Class 11 Chapter 5 States Of Matter N-pentane And 2,2 Dimethylpropane

Hydrogen bonding: As already explained in Chapter 4, a hydrogen bond is formed whenever a hydrogen atom is bonded to one or more electronegative atoms (fluorine, oxygen or nitrogen). The large electronegativity difference between the atoms leads to a highly polar covalent bond with a partial positive charge on the hydrogen atom and a partial negative charge obviously on the electronegative atom.

  • Tire electrostatic attraction between the partially positive H atom in one molecule and the partially negative atom in another molecule gives rise to a strong dipole-dipole attraction—the hydrogen bond. Hydrogen bonds are weaker than ordinary covalent bonds but stronger than other dipole-dipole attractions and London dispersion forces.
  • Hydrogen bonds have a pronounced effect on the properties of condensed phases—solid and liquids.

Generally, the energy required to overcome the intramolecular forces decreases with a decrease in molar mass. The amount of heat required to evaporate 1 mole of the hydrides in a particular group generally decreases with decrease In molar mass but H2O, HF and NH3 exhibit exceptionally high values. This is because more energy is required to overcome H-bonding in these three cases.

Basic Chemistry Class 11 Chapter 5 States Of Matter A Comparison Of The Different Intermolecular Forces As Regards Their Strength, Interaction Energy And Characterisitics

Thermal Energy: Thermal energy (i.e., heat energy) is the kinetic energy associated with the random motion of atoms and molecules. The greater the amount of thermal energy in a sample, the more vigorous is the motion of atoms and molecules. This is called thermal motion. Thermal energy is directly proportional to temperature.

  • If we increase the amount of thermal energy in a sample of matter, then either the temperature of the matter increases or the substance melts or evaporates with no change in temperature. If we decrease the thermal energy, then either the temperature decreases or the substance condenses or freezes with no change in temperature. The change in thermal energy of a substance can be observed by observing the change in temperature or state of that substance.
  • Thus, the state of a matter depends on its intermolecular forces and thermal energy. An increase in the thermal energy of a solid or liquid helps to overcome the attractive forces between the particles and the substance melts (or evaporates). Similarly, if the thermal energy is decreased the intermolecular forces play a greater role than thermal motion and a liquid (or gas) is transformed to a solid (or liquid). Now we will learn about the laws which govern the behaviour of matter in different states and thus know more about the states of matter.

Measurement Of Properties Of Gases

Let us begin our study of the states of matter with gases and liquids. The behaviour of gases is studied in terms of their mass, volume, temperature and pressure and the relationship between these properties. So, we must know how these properties are measured before we examine the behaviour of gases.

Mass: The mass of a gas can be determined by weighing a container filled with the gas and then subtracting the weight of the empty container from this weight. The number of moles or the amount of the gas can be determined from the following equation.

n = m/M,

where n = number of moles,

m = mass of gas, and

M = molar mass of gas.

The number of molecules present in a particular mass of a gas can be determined by multiplying the number of moles (in that mass of the gas) by the Avogadro constant, 6.022 x 1023 mol-1.

Volume: The volume of a substance is the space occupied by it. A gas occupies the entire space available to it, so the volume of a gas is the same as the volume of the container it occupies. The SI unit of volume is m3, but usually volume is expressed in litres (L) or millilitres (mL).

1 m3 = 103 dm3 = 106 cm3

1 mL = 1 cm3

1 L = 1000 cm3 = 1 dm3

Pressure: Pressure is force per unit area. A gas confined in a container exerts uniform pressure on the walls of the container in all directions. The pressure of the gas is the outward force exerted by the gas per unit area on the walls of the container. The pressure exerted by the gases of the atmosphere on the surface of the earth is known as atmospheric pressure.

Barometer A (mercury) barometer is a simple device used to measure atmospheric pressure. It consists of a long glass tube (longer than 76 cm) filled with mercury, which is closed at one end and inverted (the open end) into an open vessel containing mercury. The level of mercury in the tube drops until the downward pressure exerted by the column of mercury (in the tube) on the mercury in the vessel is exactly balanced by the atmospheric pressure, which acts on the open surface of the mercury in the vessel. Normally, the height of the mercury in the tube is 76 cm. It increases or decreases as the atmospheric pressure increases or decreases.

Basic Chemistry Class 11 Chapter 5 States Of Matter Mercury Barometer

Atmospheric pressure The atmospheric pressure can be calculated from the pressure exerted by the column of mercury. Let the height of the column of mercury be h cm and its area of cross section be A cm2. Then the pressure exerted by the column of mercury can be calculated as follows.

Pressure (p) = \(\frac{\text { force }}{\text { area }}=\frac{\text { mass } \times \text { acceleration }}{\text { cross-sectional area }}\)

= \(\frac{m \times g}{A}\)

where m = mass of mercury column and

g = acceleration due to gravity.

Let V be the volume of mercury in the tube and d its density.

Then p = \(\frac{V \times d \times g}{A}=\frac{A \times h \times d \times g}{A}\) = hdg (V =A x h)

Knowing the density of mercury (1.35951 x 104 kg m-3 at 0°C) and the acceleration due to gravity (9.8065 m s-2), it is possible to calculate the pressure exerted by the column of mercury 76 cm in height.

p = \((0.760 \mathrm{~m})\left(1.35951 \times 10^4 \frac{\mathrm{kg}}{\mathrm{m}^3}\right)\left(9.8065 \frac{\mathrm{m}}{\mathrm{s}^2}\right)=101,325 \mathrm{~kg} \mathrm{~m}^{-1} \mathrm{~s}^{-2}\) = 101, 325 N m-2

Thus the measurement of the atmospheric pressure does not depend upon the area of cross section of the glass tube of the barometer.

The SI unit of pressure is pascal (Pa), which is defined as the pressure exerted when a force of 1 N acts on an area of 1 m2.

1 Pa = 1 N m2.

As calculated above, 1 atm = 101,325 N m-2 = 101,325 Pa = 101.325 kPa.

The unit pascal is too small for gases and generally we express the pressure of the gas in terms of bar. The standard atmospheric pressure is 1 bar.

1 bar = 105 Pa = 100 kPa.

Pascal and bar are related to the older unit of measurement, atm, as

1 atm = 1.01325 bar = 1.01325 x 102 kPa

or 1 bar = 0.987 atm.

One atmosphere may approximately be taken to be equal to 102 kPa or 105 Pa.

1 atm is also referred to as 760 torr. The ‘torr’ is still used as a unit of pressure in some laboratories.

Manometer A manometer is used to measure the pressure of a gas. It consists of a U-tube partially filled with mercury. One of the limbs of the tube is longer than the other. The longer limb is open, while the shorter limb with its horizontal arm is connected to a closed vessel containing the gas whose pressure is to be measured.

Basic Chemistry Class 11 Chapter 5 States Of Matter An open End Manometer

The mercury in the open limb is exposed to atmospheric pressure, while the mercury in the shorter tube is subjected to the pressure of the gas. The difference in the level of the mercury in the two limbs can be used to determine the pressure of the gas.

  1. If the level of mercury is equal in both limbs, the pressure of the gas is equal to the atmospheric pressure.
  2. If the level is higher in the open tube, the pressure of the gas is higher than the atmospheric pressure (that is why the mercury gets pushed into the longer limb). Then the pressure of the gas can be determined as follows. Gas pressure (pg) = atmospheric pressure (patm) + difference in mercury levels in two columns (h)
  3. If the level of mercury is higher in the shorter tube, it means the pressure exerted by the gas is less than the atmospheric pressure. In this case, the pressure of the gas is determined as follows.

Gas pressure (pg) = atmospheric pressure (patm) – difference in mercury levels in two columns (h)

The kind of manometer we have just discussed is called an open-end manometer. In some manometers, the longer limb is closed and the space above mercury on the closed end-side is completely evacuated. They are called closed-end manometers and are used only for gases at pressures less than the atmospheric pressure.

Temperature: The temperature of a gas, like that of other substances, is measured with the help of a thermometer. A thermometer, as you must already know, uses the fact that most substances expand on heating. The substance most commonly used in thermometers is mercury. Three scales are used for the measurement of temperature.

Celsius scale The Celsius (centigrade) scale, named after the Swedish astronomer, Anders Celsius, takes the freezing point of water as 0°C and the boiling point (both points at normal atmospheric pressure) of water as 100°C. The scale is divided into 100 equal parts. Meteorologists use this scale.

Fahrenheit scale The Fahrenheit scale, named after the German physicist, Daniel Fahrenheit, takes the freezing point of water as 32°F and the boiling point of water as 212°F. The scale is divided into 180 equal parts. Clinical thermometers use this scale.

Kelvin scale The Kelvin scale, named after the British physicist, Lord Kelvin, was the result of the study of gases. You will read more about this scale later in this chapter, kelvin is the SI unit of temperature and degrees are not used while expressing temperatures on this scale. For instance, 0°C – 273.15 K, not 273.15°K. The size of the degree on a Kelvin scale is the same as on the Celsius scale. Thus, on the Kelvin scale, water freezes at 273.15 K and boils at 373.15 K at 1 bar pressure.

We can measure the amount, pressure, volume and temperature of a gas in a sealed container. The observed relationships between these four interdependent variables are expressed in the form of gas laws. These laws are the quantitative relationships between any two of these variables when the other two are kept constant.

States Of Matter Multiple Choice Questions

Question 1. At the same temperature and pressure, which of the following gases will have the highest kinetic energy per mole?

  1. Hydrogen
  2. Oxygen
  3. Methane
  4. Same in all cases

Answer: 4. Same in all cases

Question 2. The mass of 5.6 L of a gas at stp is 11 g. The gas may be

  1. PH3
  2. CoCl2
  3. NO
  4. N2O

Answer: 4. N2O

Question 3. Equal weights of ethane and hydrogen are mixed in an empty container at 25°C. The fraction of the total pressure exerted by hydrogen is

  1. 1/4
  2. 1/2
  3. 15/16
  4. 1/16

Answer: 4. 1/16

Question 4. If you take 5.0 g of each of the following gases at 87°C and 750 mm Hg pressure, which will have the least volume?

  1. HF
  2. HCl
  3. HBr
  4. HI

Answer: 2. HCl

Question 5. The density of neon will be the highest at

  1. stp
  2. 0°C, 2 atm
  3. 273°C, 1 atm
  4. 273°C, 2 atm

Answer: 2. 0°C, 2 atm

Question 6. The temperature below which a gas does not obey the ideal gas law is called the

  1. Critical temperature
  2. Inversion temperature
  3. Boyle temperature
  4. Reduced temperature

Answer: 3. Boyle temperature

Question 7. 1.0 g of H2 is heated from 300 K to 600 K in a dosed flask of volume 5 L. Which of the following statements is not correct?

  1. The tire pressure of the gas increases.
  2. The rate of collisions increases.
  3. The number of moles increases.
  4. The energy of the gaseous molecules increases.

Answer: 3. The number of moles increases.

Question 8. At constant temperature, for a given mass of an ideal gas,

  1. The ratio of pressure and volume remains constant
  2. The pressure remains constant
  3. The volume remains constant
  4. The product of pressure and volume remains constant

Answer: 4. The product of pressure and volume remains constant

Question 9. The compressibility factor for an ideal gas is

  1. 1.5
  2. 1.0
  3. 2.0

Answer: 3. 2.0

Question 10. The molecular weights of O2 and SO2 are 32 and 64 respectively. If 1 L of O2 at 15°C and 750 mm Hg contains N molecules, the number of molecules in 2 L of SO2 under the same conditions of temperature and pressure will be

  1. 2N
  2. N
  3. 2N
  4. 4N

Answer: 3. 2N

Question 11. Two separate bulbs contain gas A and gas B. The density of gas A is twice that of B. The molecular mass of A is 12 that of B. If the temperature is constant, the ratio of the pressures of A and B is

  1. 1:1
  2. 1: 2
  3. 4 :1
  4. 2:1

Answer: 3. 4 :1

 

WBCHSE Class 11 Chemistry For Bonding And Molecular Structure Notes

Bonding And Molecular Structure

The atom is considered to be the fundamental particle of an element, but apart from a few cases atoms cannot exist in the free state in nature. They combine with each other to form molecules, which are capable of independent existence. This implies that a molecule must be more stable than the individual atoms. The properties of a molecule are different from those of the constituent atoms.

  • What holds these atoms together in a molecule? There must be some force which does so. When atoms are held together in a molecule, we say that there is a chemical bond between them.
  • Not all atoms are held together by the same type of force of attraction. In fact, all atoms do not combine. It seems that only certain combinations are allowed in nature. Only certain atoms combine in certain specific ways to form molecules.
  • For example, two oxygen atoms combine to form an oxygen molecule (O2), two hydrogen atoms combine to form a hydrogen molecule (H2), and though O3 exists, H3 does not. Noble gas atoms generally do not combine.

Octet Rule

Scientists were curious to know the cause of the combination of atoms and made several attempts to explain how atoms are held together. The first satisfactory explanation was provided on the basis of the configuration of the noble gases. These gases do not combine with each other and are known to be monatomic, i.e., they exist as single atoms. Their atomic numbers and electronic configurations are as follows.

WBCHSE Class 11 Chemistry For Bonding And Molecular Structure Notes

Read and Learn More WBCHSE For Class11 Basic Chemistry Notes

Helium: 2 – 2

Neon: 10 – 2,8

Argon: 18 –  2,8,8

Krypton: 36 –  2,8,18,8

Xenon: 54 – 2,8,18,18,8

Radon: 86 – 2, 8,18,32,18,8

  • As you can see, other than helium, all the noble gases have 8 electrons in their outermost shell. Since all other elements have less than 8 electrons in their outermost shell, scientists concluded that the chemical inertness of the noble gases is related to the presence of 8 electrons in their outermost shell.
  • In other words, they concluded that if an element has 8 electrons in its outermost shell, it is chemically unreactive, or its electronic configuration is stable.
  • These observations led an American chemist, G N Lewis, to put forward a generalization known as the octet rule.
  • According to this rule, atoms of elements combine with each other so as to attain the stable configuration of 8 electrons in their outermost shell. An atom may attain this configuration by gaining, losing, or sharing electrons with other atoms.

Valency Of Nitrogen

Exceptions to the octet rule: The octet rule is a simple and useful generalisation that can explain the formation of a large number of compounds. However, it cannot be applied in some cases.

1. Hydrogen has only one electron in its valence or outermost shell, and it needs only one more electron to fill this shell and attain a stable configuration. This is possible because by acquiring one more electron, the hydrogen molecule attains a configuration like that of the noble gas helium. It may be noted that there is no octet here as the first shell can accommodate only two electrons.

2. According to the octet rule, elements of groups 1, 2, and 13 should not form covalent bonds because, having less than 4 electrons in their valence shells, they should not be able to attain stable configurations by sharing electrons. But some elements of these groups do form covalent compounds which are called electron-deficient compounds, for example, BeCl2 (beryllium has only 4 electrons in the outermost shell) and BF3 (boron has only 3 electrons).

3. The octet rule cannot explain the formation of compounds such as PCI5 and SF6 in which the central atom contains more than eight electrons. The central atom is said to have an expanded octet. An expanded octet is mostly found in the elements beyond the third period when d orbitals are available for bonding.

Basic Chemistry Class 11 Chapter 4 Bonding And Molecular Structure Exceptions To The Octet Rule

4. The basic assumption on which the octet rule is formulated is that the noble gases are inert. However, compounds of xenon like XeF2, XeF4, XeF6 have been prepared.

5. Some molecules like NO and NO2 are called odd-electron molecules as the octet rule is not applicable to all the atoms in the molecule.

The Lewis dot representation of these two molecules shows that the octet of the nitrogen atom in both molecules is incomplete (there are 7 electrons).

⇒ \(\ddot{\mathrm{N}}=\ddot{O} \quad \ddot{O}=\dot{\mathrm{N}}^{+}-\ddot{\mathrm{O}}^{-}\)

Valency Of Nitrogen

Lewis Structure The Concept Of Valence Electrons

Another observation that helped scientists understand the ways in which atoms combine was that atoms which f have the same number of electrons in their outermost shells exhibit similar chemical properties. This led them to conclude that only the electrons in the outermost shell participate in the process of chemical combination.

  • The electrons in the inner shells do not participate in bonding. The outermost shell electrons are called valence electrons. The chemical properties of an element depend on the number of valence electrons.
  • Lewis introduced a simple notation to represent the valence electrons in an atom. In this notation the valence electrons are represented by dots (or crosses) surrounding the chemical symbol of the element.
  • These symbols, called Lewis symbols or electron dot symbols, do not show the electrons in the inner shells. The chemical symbol of the element represents the nucleus and the inner electrons. The Lewis symbols for the elements of the second period are given below.

Basic Chemistry Class 11 Chapter 4 Bonding And Molecular Structure Lewis Structure

The number of dots in the Lewis symbol of an element indicates the number of electrons in the outermost shell (valence shell) electrons. Consider the symbols for Li, Be, B, and C. The number of dots in these symbols indicates the usual valence of these elements. Thus lithium is monovalent, beryllium is divalent, boron is trivalent and carbon is tetravalent.

  • The valencies of nitrogen, oxygen, and neon are 3,2 and 0 respectively. The valence of fluorine is 1. That is to say the valence of these elements can be obtained from the Lewis symbols by subtracting the number of dots from 8.
  • Whatever may be the drawbacks of the octet rule, most atoms do tend to combine in order to attain a more stable configuration of 8 electrons in the valence shell. They do so by the redistribution of their valence electrons. This can occur in one of two ways.

Valency Of Nitrogen

  1. By the complete transfer of one or more electrons from one atom to another. The chemical bond thus formed is called an ionic bond.
  2. By the sharing of electrons between atoms. The bond formed is called a covalent bond.

Electrovalent Or Ionic Bond

Kossel, while studying chemical bonding, observed that the highly electronegative halogens form a negative by gaining an electron whereas the highly electropositive alkali metals form a positive ion by readily losing an electron. The elements of the two groups (halogens and alkali metals) gain or lose electrons respectively and attain a stable outer shell configuration of eight electrons.

The noble gases (Group lb elements) have the stable outer shell configuration of eight electrons except helium, which has just two electrons. Kossel explained that the negative and positive ions (formed by gain or loss of electrons) are hold together by electrostatic attraction among them. This electrostatic attraction was later termed the electrovalent bond.

  • Kossel’s observations led to the understanding of ionic bonding in ionic compounds. It also provided the basis of the concept of electron transfer in ion formation and thereafter the formation of ionic compounds. Besides providing a concept of ionic bonding, Kossel realised that not all compounds are formed by electron transfer between the atoms.
  • Atoms which contain 1, 2, or 3 electrons in their valence shell have a tendency to lose electrons to acquire a stable configuration. It is easier for such atoms to lose 1,2 or 3 electrons than to gain 7,6 or 5 electrons respectively. Similarly, atoms that have 5, 6, or 7 valence electrons have a tendency to complete their valence shell by gaining 3,2 or 1 electrons respectively.
  • Atoms are electrically neutral as they possess an equal number of electrons and protons. However, when an atom loses electrons to attain a stable configuration, it becomes positively charged because it contains a greater number of protons than electrons.

Basic Chemistry Class 11 Chapter 4 Bonding And Molecular Structure Electrovalent Or Ionic bond

A positively charged atom is called a cation. When, on the other hand, an atom gains electrons to attain a stable configuration, it becomes negatively charged because it has a greater number of electrons than protons. A negatively charged atom is called an anion.

  • When one atom acquires the electrons which another atom loses, the oppositely charged ions so formed are drawn together by an electrostatic force of attraction. When two ions are held together in this way, an ionic bond or an electrovalent bond is said to exist between them. In other words, the bond between oppositely charged ions, formed by tire transfer of electrons from one atom to another, is called an ionic bond.
  • Such bonds are generally formed between a metal and a nonmetal (as discussed above, alkali metals and halogens respectively). For example, the sodium atom (atomic number 11) has only one electron in its valence shell. In order to acquire the nearest noble gas configuration (2, 8) it has to lose one electron.
  • The chlorine atom (atomic number 17) has seven electrons in its valence shell and it is easier for it to gain an electron to acquire the nearest noble gas configuration (2, 8, 8). So, the sodium atom transfers its valence electron to the chlorine atom, resulting in tire formation of a sodium ion (Na+) and a chloride ion (Cl), which are held together by a force of electrostatic attraction.

The number of electrons which an atom loses or gains while forming an ionic bond is called its electrovalency. Atoms that tend to lose electrons are called electropositive because they form positively charged ions after losing electrons. Atoms which gain electrons are called electronegative because they form negatively charged ions after gaining electrons. One more example of an ionic compound is given here.

Basic Chemistry Class 11 Chapter 4 Bonding And Molecular Structure Electro Or Ionic Bond 1

Ionic bonds are formed due to electrostatic forces of attraction, which are non-directional. An ion has a uniform electrostatic field of influence around it, i.e., it attracts ions all around it. The attraction between two ions depends on the distance between them, and not on the direction of one from the other.

  • Each positively charged ion attracts several negatively charged ions around it and each negative ion attracts several positive ions around it. The number of oppositely charged ions a particular ion will attract depends on its size and charge.
  • This aggregation of oppositely charged ions around one ion results in the formation of a three-dimensional aggregate of ions called an ionic crystal. Oppositely charged ions alternate in a regular geometrical pattern in such a crystal. The cations and anions are held together in the crystal by attractive forces.
  • An ionic compound consists of an aggregate of ions. These ions held together by an ionic bond cannot be looked upon as a molecule. Thus, an ionic compound cannot be assigned a molecular formula. For example, the formula of sodium chloride can be written as NaCl or Na+Cl. This is its empirical formula and not its molecular formula.
  • The empirical formula of an ionic compound can be derived from the valency of the elements or the ratio of cations to anions. In NaCl, the ratio is 1:1. So, the (empirical) formula of sodium chloride is NaCl.

Basic Chemistry Class 11 Chapter 4 Bonding And Molecular Structure The Structure Of Sodium Chloride Crystal

Formation of an ionic bond: The formation of an ionic bond broadly involves the formation of the gaseous cation, the gaseous anion, and the packing of ions to form the ionic solid.

Formation of cations and anions You have already studied in Chapter 3 that energy is required to remove an electron from an isolated neutral gaseous atom, and is defined as the ionisation enthalpy of the element. Thus, the formation of a positive ion or removal of electron(s) involves the process of ionisation. Let us consider the formation of NaCl.

⇒ \(\mathrm{Na}(\mathrm{g}) \rightarrow \mathrm{Na}^{+}(\mathrm{g})+\mathrm{e}^{-} ; \Delta H\) (Ionisation enthalpy)

On the other hand, chlorine atom accepts an electron to form a negative ion (Cl). The enthalpy change in this reaction involving addition of electron(s) is termed as electron gain enthalpy.

Limitations Of Octet Rule For Class 11

⇒ \(\mathrm{Cl}(\mathrm{g})+\mathrm{e}^{-} \rightarrow \mathrm{Cl}^{-}(\mathrm{g}) ; \Delta H\)(Electron gain enthalpy)

The ionisation enthalpy of an atom is always positive (energy is always required to remove an electron) but the electron gain enthalpy of an atom may be positive or negative, depending on the nature of the element.

  • Considering the enthalpy changes during formation of ions, we may conclude that ionic bonding is most likely to occur between atoms with low ionisation enthalpies and high negative electron gain enthalpies.
  • Generally, ionic compounds are formed by cations from metallic elements (metals have low ionisation enthalpies) and anions from nonmetals (nonmetals have high negative electron gain enthalpies).

The conditions required to form an ionic bond are best satisfied in alkali halides. The cation NH+4 (ammonium ion) is an exception, it is made up of two nonmetals.

Packing of oppositely charged ions The last step in the formation of an ionic compound is the packing of negative and positive ions to form a lattice. The energy released in this process is known as lattice energy.

More formally, the energy released in the formation of 1 mole of an ionic solid by the packing of oppositely charged ions is called lattice enthalpy. The lattice enthalpy may also be defined as the energy needed to separate one mole of a solid ionic compound into the constituent gaseous ions. The lattice enthalpy of sodium chloride is 788 kJ mol-1. This means that 788 kJ of energy is needed for the following reaction to occur.

⇒ \(\mathrm{NaCl}(\mathrm{s}) \rightarrow \mathrm{Na}^{+}(\mathrm{g})+\mathrm{Cl}^{-}(\mathrm{g})\)

The higher the value of the lattice enthalpy of an ionic compound, the more stable it is, and the more readily will such a compound be formed. Ionic compounds are held together by electrostatic attraction and the force of attraction depends directly on the magnitude of the charges and inversely on the square of the distance between the charges.

F = \(\frac{q_1 q_1}{d^2}\)

The greater this force, the more the chance of formation of the ionic compound. In other words, a greater magnitude of charge and a smaller ionic size favours the formation of an ionic solid. A smaller ionic size would mean a smaller internuclear distance.

  • For stable ionic bonding, the total energy released during the formation of the crystal lattice should be greater than the energy required for the formation of ions.
  • In the case which we have just considered, the first ionisation enthalpy for sodium is 495.8 kJ mol-1 and the electron gain enthalpy for chlorine is -348.7 kJ mol-1. Their sum comes to 147.1 kJ mol-1 which is actually the energy required for the formation of ions. This energy is much less than that released during the formation of the crystal lattice, which is equal to 788 kJ mol-1. Thus, a greater lattice enthalpy implies greater stability of the compound.

Properties of ionic compounds: By and large, ionic compounds have certain common characteristics.

Limitations Of Octet Rule For Class 11

Physical state They are usually crystalline solids, in which the ions are arranged in a well-defined geometrical pattern. The force of attraction between the oppositely charged ions is very strong, which is why these compounds exist in the solid state at room temperature.

Melting and boiling points Ionic compounds generally have high melting and boiling points. This is because a large amount of energy is required to overcome the strong electrostatic force of attraction which holds the ions together in such compounds.

Electrical conductivity Ionic compounds are not good conductors of electricity in the solid state because the ions are held in fixed positions in the crystal lattice by electrostatic force of attraction between ions. The ions are, thus, not free to move. However, they become free to move in the molten state and in aqueous solutions, and carry charge. So ionic compounds are good conductors of electricity in the molten or dissolved state.

Solubility Ionic compounds are soluble in water and other polar solvents. Such solvents can weaken the force of attraction that holds together the ions in an ionic compound. Such compounds are insoluble in nonpolar solvents like benzene and carbon tetrachloride.

Ionic reactions Chemical reactions between ionic compounds are called ionic reactions. Such reactions take place between the ions of the two compounds produced in an aqueous solution. These reactions involve oppositely charged ions which combine readily, so they occur almost instantaneously.

 

Hydrogen Bond

The hydrogen atom has a unique structure. It has only one proton and one electron. When a hydrogen atom forms a covalent bond with a highly electronegative atom, the bonded electron pair shifts towards the latter. Consequently, the nucleus of the hydrogen atom gets exposed and behaves like a proton.

It exerts a strong electrostatic force of attraction on the electronegative atom of an adjacent molecule. This force of attraction between the (covalently bonded) hydrogen atom of one molecule and the electronegative atom of another molecule is called a hydrogen bond. It is represented by a dotted line.

Basic Chemistry Class 11 Chapter 4 Bonding And Molecular Structure Hydrogen Molecule Denoted By Dotted Lines

The following conditions are necessary for hydrogen bonding.

1. The molecule must contain a highly electronegative atom linked to the hydrogen atom. The greater the electronegativity of the atom linked to the hydrogen atom, the stronger is the hydrogen bond.

2. The size of the electronegative atom should be small. The smaller the size, the greater is the attraction between the atom and the hydrogen atom and the stronger is the bond.

Only F, O, and N satisfy both these conditions.

Fluorine, having the highest value of electronegativity, forms the strongest hydrogen bond.

Basic Chemistry Class 11 Chapter 4 Bonding And Molecular Structure Flourine Having Highest Value Of Electronegativity

The water molecule contains the highly electronegative oxygen atom linked to the hydrogen atom. The oxygen atom attracts the shared pair of electrons more strongly and this end of the molecule becomes negative, while the hydrogen-end becomes positive.

Basic Chemistry Class 11 Chapter 4 Bonding And Molecular Structure Ammonia Electronegative Nitrogen Atom

In ammonia, the more electronegative nitrogen atom attracts the shared electrons towards itself, leaving the hydrogen atom positively charged. This hydrogen atom forms a hydrogen bond with the nitrogen atom of another molecule.

Nature of hydrogen bond: The hydrogen bond is a weak bond. Unlike the covalent bond, which involves the sharing of electrons by two atoms of elements of the same or different electronegativities, the hydrogen bond arises due to the interaction between dipoles.

The strength of the hydrogen bond lies between those of the van der Waals force and the covalent bond. The dissociation energy of the hydrogen bond depends upon the electronegativity of the other atom. The bond energy is highest in H—F because fluorine is the most electronegative element.

Impact of hydrogen bonding: Although the hydrogen bond is weak, it influences the physical properties of the substances in which it acts. Association The hydrogen bond links molecules to form aggregates of molecules.

Basic Chemistry Class 11 Chapter 4 Bonding And Molecular Structure Impact Of Hydrogen Bonding

For example, HF molecules become linked by hydrogen bonding and the formula of hydrogen fluoride can be written as (HF)π. This changes the molecular mass of the compound. For instance, carboxylic acids exist as dimers because of hydrogen bonding and their molecular mass is double the molecular mass predicted by their simple formula. The molecular mass of acetic acid is 120 but its mass according to its simple formula should be 60.

Dissociation In an aqueous solution, hydrogen fluoride dissociates and produces the difluoride ion (HF2) instead of the fluoride ion (F). This is due to H-bonding in HF. This explains why KHF2 exists, while KHCl2, KHBr2, and KHI2 do not. The other halogens cannot form hydrogen bonds because of low electronegativity and bigger size.

High melting and boiling points Compounds in which the molecules are linked by hydrogen bonds have much higher melting and boiling points than compounds formed by other members of their groups. Tins is because a greater amount of energy is required to break the hydrogen bonds.

  • Let us consider the hydrogen halides, for example. Hydrogen fluoride exists as a liquid (high boiling point) at room temperature, while HCl is a gas. The boiling points of the hydrogen halides decrease as molecular mass decreases, but there is a sudden increase in the boiling point of HF because of the presence of the hydrogen bond.
  • Similarly, H2O is a liquid, but H2S is a gas at room temperature. In fact water has an abnormally high boiling point as compared to the other hydrides of its group. NH3 has an abnormally high boiling point as compared to the hydrides of the other elements of its group.
  • This difference is seen among organic compounds too. For example, ethanol has a higher boiling point than diethyl ether because of the presence of hydrogen bonding in the former. Both compounds have oxygen atoms, but in diethyl ether, the oxygen atom is not bonded to hydrogen.

Basic Chemistry Class 11 Chapter 4 Bonding And Molecular Structure Hydrogen Bonding In Ethanol And Diethyl Ether

Solubility Covalent compounds are generally insoluble in polar solvents like water. However, compounds which can form hydrogen bonds with water are soluble in water, example, alcohol, acetone, and urea.

Similarly, ammonia (NH3) dissolves in water but PH3 (phosphine) does not. This is because of the ability of the nitrogen atom to form a hydrogen bond with water.

Viscosity Viscosity is the resistance offered to the flow of a liquid. The viscosity of a liquid increases if there is hydrogen bonding between its molecules because this is an additional intermolecular force which aggregates molecules. For example, glycerol is more viscous than ethylene glycol and ethyl alcohol. All alcohols have at least one —OH group which can form a hydrogen bond. Glycerol has three —OH groups, ethylene glycol has two, while ethyl alcohol has only one.

Density of ice Ice has a lower density than water, though hydrogen bonding is present in both water and ice. In ice, each oxygen atom is tetrahedrally bonded with four hydrogen atoms. Two hydrogen atoms are bonded by covalent bonds and another two through hydrogen bonds. This gives rise to an open cage-like structure, which occupies a larger volume than does water. In the liquid, the water molecules are more closely packed. When ice melts, this cage-like structure collapses and the water molecules come closer to each other. Thus, for the same mass of water, the volume decreases and density increases.

Types of hydrogen bonding: There are two types of hydrogen bonding—intermolecular and intramolecular.

Intermolecular When hydrogen bonding takes place between different molecules of the same or different compounds, it is called intermolecular hydrogen bonding. For example, HF, H2O, NH3, and alcohol.

Basic Chemistry Class 11 Chapter 4 Bonding And Molecular Structure O-nirophenol And Salicyclic Acid

Intramolecular Hydrogen bonds between atoms of the same molecule are called intramolecular hydrogen bonds. Such bonds are formed in many organic compounds, example, o-nitrophenol and o-hydroxy benzoic acid (salicylic acid).

Intramolecular H-bonding prevents the association of molecules, making the molecule contract. Hence, this kind of H-bonding decreases melting and boiling points and solubility. For example, o-nitrophenol has a lower boiling point than p-nitrophenol.

Resonance

The properties of certain molecules containing a π bond cannot be explained by writing one Lewis structure. For example, the structure of ozone can be written as either (1) or (2) here, but neither can explain its experimentally determined properties.

Basic Chemistry Class 11 Chapter 4 Bonding And Molecular Structure Resonance

  • According to either of these structures, the central oxygen atom is bonded to one oxygen atom by a double bond and the other oxygen atom by a single bond. Since a double bond (121 pm) is shorter than a single bond (148 pm), the two bond lengths in this molecule should be different.
  • However experimental evidence shows that the bonds are equal and that the bond length is 128 pm, between the length of a single bond and that of a double bond. Thus, neither structure (1) nor (2) can explain why O3 has two equal bonds.
  • It is assumed that tire actual structure is between the two Lewis structures. This phenomenon is called resonance and the two (or more) individual structures are called resonating structures or canonical forms. To define this more clearly, when a molecule can be represented by more than one Lewis structure none of which can individually explain all its observed properties, the actual structure of the molecule is the intermediate of the various Lewis structures and is called the resonance hybrid.

This is a theoretical concept. Tire-resonating structures have no physical reality, that is to say, they do not actually exist. Only the hybrid structure exists. There is no equilibrium between the canonical forms. In theory the various resonating structures have the following characteristics.

  1. The same arrangement of atoms
  2. The same of number of paired and unpaired electrons, but different electronic arrangement
  3. They have nearly the same energy but the energy of the resonance hybrid is less than that of each of the canonical forms. Thus, resonance stabilises the molecule
  4. The same positions of sigma bonds but different positions of pi bonds

Some examples are given below.

1. Carbon dioxide (CO2) The C—O bond length in the molecule is experimentally determined as 115 pm. The value is between the length of C=O (121 pm) and C≡O (110 pm). Therefore, the structure of CO2 can be described as a resonance hybrid of three canonical forms.

∴ \(: \mathrm{O}=\mathrm{C}=\mathrm{O}: \longrightarrow \stackrel{+}{\mathrm{O}} \equiv \mathrm{C}-\overline{\mathrm{O}}: \longrightarrow: \overline{\mathrm{O}}-\mathrm{C} \equiv \stackrel{+}{\mathrm{O}}:\)

2. Carbonate ion (\(\mathrm{CO}_3^{2-}\)) Since the experimentally determined bond length values show that all the carbon- oxygen bonds are equal in a carbonate ion, its structure can be described as the resonance hybrid of the three canonical forms as follows.

Basic Chemistry Class 11 Chapter 4 Bonding And Molecular Structure Carbonate Ion

3. Phosphate ion \((\left(\mathrm{PO}_4^{3-}\right))\) Experimental findings show that all the phosphate oxygen bonds are equal in the phosphate ion. Therefore, the structure of the ion is best described as the resonance hybrid of the following four canonical forms.

Basic Chemistry Class 11 Chapter 4 Bonding And Molecular Structure Phospahte Ion

4. Benzene (C6H6) It has been found that all carbon-carbon bond lengths are identical and the two important canonical forms are

Basic Chemistry Class 11 Chapter 4 Bonding And Molecular Structure Benzane