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

All living beings for survival need air. Air is the commonly used name for the mixture of gases that create the Earth's atmosphere. The gas is the primary element, mixed with Oxygen, vapour, greenhouse and trace gases. Chapter 4 intricately explains air by explaining the composition of the atmosphere, the structure of the atmosphere, weather and climate, etc. Through this chapter, we learn that nitrogen is the most abundant gas in the air and how when we inhale, we take some amount of nitrogen into our lungs and exhale it and how it helps plants as plants need nitrogen for their survival. However, they cannot take nitrogen directly from the air and thus take help of bacteria living in the soil and roots system of some plants that take nitrogen from the air and change their form so that plants can use it.

The chapter also explains the layers in which our atmosphere is divided into starting with the Troposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere in which the troposphere is the layer in which the air we breathe exists and is, therefore, a most important layer of the atmosphere. Its average height is 13 km and almost all-weather phenomenon like rainfall, fog and hailstorm occur in this layer. Above the troposphere, there lies the stratosphere which extends up to a height of 50 km and is almost free from clouds and associated weather phenomenon, making ideal conditions for flying aeroplanes while the layers also protect us from the harmful effect of the sun rays.