Exercise Question:

Que1: To walk through a waterlogged area, you usually shorten the length of your dress byb folding it. Can this change be reversed?

Ans: yes, by unfolding the dress this  change can be reversed.

Que2: You accidentally dropped your favourite toy and broke it. this is a change you did not want. Can this change be reversed?

Ans: No, it cannot be reversed, so it is an irreversible change.

Que3: Some change are listed in the following tables. 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 piece of wood    
2.            The melting of ice candly
3.            Dissolving sugar in water
4.              The cooking of food
5.            The ripening of a mango
6.               Souring of milk

Ans: 

 S.No.                  Change                                 Can be reversed (Yes/No)    

1.          The sawing of piece of wood                          No
2.            The melting of ice candly                             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

Que4: A drawing sheet changes when you draw a picture onit. Can you reverse this changed?

Ans: It is all depands on situations: 

1. By erasing the drawing we can undo the change. for example, if we draw with the help of pencil, we can erase the drawing by using an eraser. Then, it is a reversible change.
2. If we draw using a pen, we cannot erase the drawing.  Then this changed cannot be reversed, so it is irreversible change.

Que5: Give example to examples the difference between changed that can or cannot be reversed.

Ans: 

Examples of Reversible changes:

1. Melting of Ice into water. By freeing the water we can obtain ice again.
2. Folding a paper: By unfolding it, we can undo the change.
3. Hot milk to cold milk: By Boiling milk, we can make it warm.

Example of Irreversible changes:

1. Buring of candle.
2. Bursting of crackers.
3. Cutting of trees.

Que6: A thick coating of a paste of plaster pf paris(POP) is applied over the bandage on a fractured bone. it becomes hard on dying to keep the fractured bone immobilised. Can the change in POP be reversed?

Ans: When water is added to POP, it undergoes a chemical changes. its composition changes and is converted into another substance. since it is a chemical change, so it cannot be reversed?

Que7: 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?

Ans: Dueto water, cement hardens ans its composition changes. since it is a chemical change which canot be reversed.