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?

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

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

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

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.