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

NCERT TEXTBOOK EXERCISES

Question 1. To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?
Answer : Yes, this change can be reversed.

Question 2. You accidentally dropped your favourite toy and broke it. This is a change you did not want. Can this change be reversed?
Answer : No. This change cannot be reversed. Breaking a toy is an irreversible change.

Question 3. Some changes are listed in the following table. For each change, write in the blank column, whether the change can be reversed or not.

S.No.	Change	Can be reversed (Yes/No)
1.	The sawing of a piece of wood
2.	The melting of ice candy
3.	Dissolving sugar in water
4.	The cooking of food
5.	The ripening of a mango
6.	Souring of milk

Answer :

S.No.	Change	Can be reversed (Yes/No)
1.	The sawing of a piece of wood	No
2.	The melting of ice candy	Yes
3.	Dissolving sugar in water	Yes
4.	The cooking of food	No
5.	The ripening of a mango	No
6.	Souring of milk	No

Question 4. A drawing sheet changes when you draw a picture on it. Can you reverse this change?
Answer : No. We cannot reverse this change. Because we cannot get a fresh drawing sheet once a picture is drawn on it. But if the pencil is used to draw the picture, we can reverse the change.

Question 5. Give examples to explain the difference between changes that can or cannot be reversed.
Answer : One way we can group changes is to see if they can be reversed or not.
1. Changes that can be reversed: In such changes, we can return back to the original position if the cause of change is withdrawn; for example,
(a) heating of milk,
(b) drying of clothes,
(c) knitting a sweater,
(d) stretching a rubber band,
(e) melting of ice, etc.
2. Changes that cannot be reversed: The changes in which we cannot go back to the original position, even if we withdraw the cause of change; for example,
(a) boiling of egg,
(b) making curd from milk,
(c) making flour from grain,
(d) the flowering of a bud,
(e) producing biogas from cow dung, etc.

Question 6. A thick coating of a paste of Plaster of Paris (POP) is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilized. Can the change in POP be reversed?
Answer : No, it’s not a reversible change.

Question 7. A bag of cement lying in the open gets wet due to rain during the night. The next day the sun shines brightly. Do you think the changes, which have occurred in the cement, could be reversed?
Answer : No, it’s not a reversible change.