Question 1. To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?
Solution 1. Yes, by unfolding the dress it will retain its original length.
Question 2. You accidentally dropped your favourite toy and broke it. This is a change you did not want. Can this change be reversed?
Solution 2. The broken toy would not be the same again. So, this change cannot be reversed.
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 |
Solution 3.
| 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?
Solution 4. No, a drawing sheet can not be the same again after you draw a picture on it with any colouring material or dark pencils but this change can be reversed if you draw the picture by soft pencils.
Question 5. Give examples to explain the difference between changes that can or cannot be reversed.
Solution 5. Following are examples of reversible changes and irreversible changes.
| Reversible changes | Irreversible changes |
| Stretching of spring (it retains its original size when you leave it) | Cooking of food is irreversible |
| Inflation of balloon (you can blow it again and again) | Growth of a plant (growth is reversible) |
| Folding of paper sheets | Burning of fuels |
| Melting of ice cubes | Burning of paper sheets |
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 immobilised. Can the change in POP be reversed?
Solution 6. A chemical change cannot be reversed hence the change in POP cannot be reversed as it is a chemical 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?
Solution 7. No, this type of chemical change cannot be reversed.