1. What’s the solution ? 

(a) We need to make a sherbet quickly for some guests. But we only have sugar candy in the house.

Ans: We can crush sugar candy into a fine powder. When the powder is fine, it will quickly dissolve in water. Therefore, we can make sherbet quickly.

(b) We need to rub salt on a corncob but only salt crystals are available.

Ans: All objects are made of substances, which are made up of tiny particles. We obtain salt by the evaporation of seawater. Salt crystals cannot be rubbed on corncobs; therefore, they should be ground into a powder. The powdered salt can be easily rubbed onto the corncob.

2. Use your brain power !

(a) Why do tablets of camphor decrease in size day by day?

Ans: Tablets of camphor are in a solid state. Camphor has the property to turn into a gaseous state directly from a solid state. Therefore, camphor decreases in size gradually.

(b) How do we save fuel by using public transport ?

Ans: If people drive cars instead of using public transport while going to work, more fuel will be burned, as each car will burn the fuel to release energy and work. However, if public transport is used, we need to use fuel only for one transport vehicle. Hence, it will save a lot of fuel if people use public transportation.

3. Answer the following questions. 

(a) When and why do clothes smell of naphthalene?

Ans: Naphthalene is continuously converted into small particles in the gaseous state. Such small particles from the balls settle on the clothes. So the clothes smell of naphtalene.

(b) In which states is water found in nature? 

Ans: Water is found in all three states of nature: the solid, liquid, and gaseous states. Ice is the solid state of water. Water in lakes, sea, etc. is in a liquid state, and steam or vapour is the gaseous state of water.

(c) What is the difference between the solid, liquid and gaseous states of a substance ? 

Ans: