NCERT Solutions for Class 7 Geography Social Science Chapter 4 - Air

(i) The blanket of air surrounding the earth is called the atmosphere. The atmosphere primarily comprises nitrogen and oxygen in bulk and other gases like carbon dioxide, helium, ozone, etc. in less quantities. All living beings on earth depend on the atmosphere for their survival.

(ii) The two gases that make the bulk of the atmosphere are:

1. Oxygen (21%)

2. Nitrogen (78%)

(iii) Carbon dioxide is the gas that creates the greenhouse effect in the atmosphere.

(iv) The hour-to-hour or the day-to-day condition of the atmosphere is called weather. Weather can change dramatically from day-to-day. It may be classified as hot, dry, cold or wet.

(v) The three types of rainfall are as follows:

1. Convectional rainfall

2. Orographic rainfall

3. Cyclonic rainfall

(vi)  Air pressure is defined as the pressure exerted by the weight of air on the earth’s surface. The air pressure decreases as height increases and is the highest at the sea level.

(i) c

(ii) a

(iii) b

(iv) b

(v) b

(i) Wet clothes take longer time to dry on a humid day because the amount of water in the air is more on a humid day than on a sunny day. Due to this, the rate of evaporation decreases and air soaks in less water from the clothes.

(ii) Insolation is the incoming solar energy intercepted by the earth. Amount of insolation decreases from the equator toward poles because sun rays fall vertically on the equator and slant on the poles.