Q 1.

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

SOLUTION:

Yes, it can be reversed. The folded dress can be unfolded.

Q 2.

You accidentally dropped your favourite toy and broke it. This is a change you did not want. Can this change be reversed?

SOLUTION:

No, this change (breaking of toy) cannot be reversed.

Q 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

SOLUTION:

(1) No; (2) Yes; (3) Yes; (4) No; (5) No; (6) No

Q 4.

A drawing sheet changes when you draw a picture on it. Can you reverse this change?

SOLUTION:

No, we cannot get the same drawing sheet back if we draw the picture on it with pen or paint. It can be reversed by rubbing the picture with eraser if drawn with a pencil.

Q 5.

Give examples to explain the difference between changes that can or cannot be reversed.

SOLUTION:

(i) Folding of a paper is a reversible change because paper can be unfolded to get it back.
(ii) Burning of paper is an irreversible change because we cannot get back the paper after burning it.
(iii) Mimosa (touch-me-not) leaves collapse on touching and open up on removing finger. Hence, it is a reversible change.
(iv) Growth of a plant is irreversible since it cannot be reversed.

Q 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 immobilised. Can the change in POP be reversed?

SOLUTION:

No, once the plaster is dried, it becomes hard and cannot be reversed back to paste form.

Q 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?

SOLUTION:

No, when the water is mixed with the cement, it becomes hard and the change cannot be reversed.