Question

Assertion: Snow is a better insulator than ice.
Reason: Snow contains air pockets and the air is a good insulator of heat.
A) Both assertion and reason are correct and the reason is the correct explanation of assertion.
B) Both assertion and reason are correct and the reason is not the correct explanation of the assertion.
C) The assertion is correct but the reason is incorrect.
D) Both assertion and reason are incorrect.

Answer 1

A substance is considered to be a good insulator of heat if it does not allow the flow of heat through it. Snow and ice may seem similar but they can be considered to be two different variations of the same substance, water and they have different physical properties. Ice is the solid form or solid phase of water while snow is porous in nature.

Complete step by step solution:
Step 1: Try to explain the formation of snow to get a better understanding of its physical nature.

As the temperature of the atmosphere reaches $0^\circ {\text{C}}$ , water vapours present in the air freeze to form tiny particles of ice. Many such particles will combine to form a cotton-like structure called snow. So snow will be a combination of water molecules and air particles. More specifically, the air in the atmosphere gets filled into the porous structure of the snow.

Now ice, on the other hand, is a compact structure which contains only water molecules. It is the solid phase of water. It does not contain pores which can be filled by air and ice is denser than snow.

Air is a known insulator of heat. So the presence of air in snow, makes it a better insulator than ice.

So both assertion and reason are correct and the reason correctly explains the assertion.

Hence the correct option is A.

Note: Air by itself, may not be a great insulator of heat. But when it can be trapped in small spaces like the pores present in snow, it resists the flow of convection heat currents. This makes it a good insulator of heat. Now, in terms of density, ice will be denser than snow, since it is a solid form. But the density of the two substances has no contribution to the fact that snow is the better insulator of the two.