Table of Contents
NCERT Class 6 Science Chapter 5, Changes Around us, Exercise question Solution
1. To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?
Answer: We shorten the length of the dress here to reduce the resistance from water. This is reversible as after coming out from the waterlogged area we unfold the dress into the original state.
2. You accidentally dropped your favorite toy and broke it. This is a change you did not want. Can this change be reversed?
Answer: Breaking a toy is an irreversible thing. We cannot get back the toy in the original state unless we replace the broken part.
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.
Answer:
The sawing of a piece of wood: Irreversible.
The melting of ice candy: Reversible.
Dissolving sugar in water: Reversible.
The cooking of food: Irreversible.
The ripening of a mango: Irreversible.
Souring of milk: Irreversible.
4. A drawing sheet changes when you draw a picture on it. Can you reverse this change?
Answer: Drawing a sheet using colour or ballpoint pen is irreversible. However, if we use a pencil, we can erase them with erase and get back the drawing sheet in the previous state.
5. Give examples to explain the difference between changes that can or cannot be reversed.
Answer: We can reverse many things which we see in daily life. For example, we can freeze the water to get ice and defreeze the ice to get water.
However, the opposite is also true. We cannot reverse many a thing which we see around. For example, we can not reverse the ripening of fruits, souring of milk.
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 immobilized. Can the change in POP be reversed?
Answer: Water reacts with plaster of Paris and forms hard substances. This is irreversible in nature.
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: Cement reaction with water is chemical in nature. We cannot reverse it. Imagine a situation if cement in our build gets reverse than what will happen!
