# Class 6 | Science | Chapter 6 | Changes around us | NCERT Solutions

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 1 Yes, by unfolding the dress 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 2 No, it cannot be reversed, so it 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

 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 4 If we draw with the help of pencil, we can erase the drawing by using an eraser. Then, it is a reversible change.

If we draw using a pen, we cannot erase the drawing. Then this change cannot be reversed, so it is irreversible change.

Question 5 Give examples to explain the difference between changes that can or cannot be reversed.

Answer 5) 1) The folding of paper is a reversible change whereas the cutting of paper is an irreversible change.

2)The rolling of roti out of dough is a reversible change whereas baking of roti is an irreversible change.

3) If we draw a picture using a pencil sketch, then the change is reversible. However, if the picture is drawn using an oil colour, sketch, water colours or pen, then the change is irreversible.

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?

Answer 6 Plaster of Paris (POP) is a white, powdery substance which immediately sets to a hard mass on adding water to it. In hospitals, a thick coat of the paste of plaster of Paris is applied over the bandage on the fractured bone of a person. POP sets and becomes hard on drying and keeps the fractured bone in place to get the joined properly. Thus, the setting of plaster of Paris on mixing water is an irreversible 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 7 Due to water, cement hardens and its composition changes. Since it is a chemical change which cannot be reversed.