NCERT Solutions for Class 6 Science Chapter 6 - Changes Around Us

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Chapter 6 - Changes Around Us Exercise 51

Solution 1

Yes, because the folded portion of the dress can be unfolded. It is a reversible physical change.

Solution 2
No, this change cannot be reversed. But, breaking of toy does not bring any change in the composition of the toy. Some physical changes are irreversible but they do not bring any change in the composition of material.
Solution 3

Physical changes can be reversed but chemical changes cannot be reversed.

S.No.

Change can be reversed or not

Yes/ No

1.

2.

3.

4.

5.

6.

The sawing of a piece of wood

The melting of ice candy   

Dissolving sugar in water

The cooking of food

The ripening of a mango

Souring of milk

No

Yes

Yes

No

No

No

Solution 4
If we draw a picture on a drawing sheet with a pencil, we can get back the original drawing sheet by erasing the drawing with an eraser. In this case, the change can be reversed.
However, if we draw with a pen, then the original drawing sheet cannot be obtained back because we cannot erase ink. Hence, in this case, the change cannot be reversed.
Solution 5
To explain the differences between changes that can or cannot be reversed, some examples are given below:
(i) If we inflate a balloon, the size and shape of the balloon undergoes a change. However, the original size and shape of the balloon can be obtained back by allowing the air to escape from the balloon. This means that the change that occurs by inflating a balloon can be reversed. But, if the balloon bursts after being inflated, then its original size and shape cannot be obtained back. Thus, in this case, the change cannot be reversed.
(ii) If we fold a piece of paper, then the shape and size of the paper undergoes a change. In this case, the original shape and size of the original paper can be obtained back. Thus, this change can be reversed. However, if we cut the piece of paper, the change in the shape and size of the paper cannot be reversed.
(iii) After we roll out a chapatti from a ball of dough, the chapatti can be converted back into a ball. Thus, the change occurring here can be reversed. But, if we cook the chapatti on a tawa, then it cannot be converted back into a ball of dough. Thus, the change is irreversible.
Solution 6
No, the change in POP can not be reversed because on addition of water, it changes to another substance which on drying becomes hard.
Solution 7
No it can not be reversed.