The invisible gaseous substance surrounding the earth, a mixture mainly of oxygen and nitrogen.

Air: NCERT Solutions, Class 7, SST, Chapter 4
Air is a mixture of gases that surround the Earth. It is essential for life on our planet and plays a crucial role in various natural processes. Here are some key points about air:

Composition of Air:
- Air is primarily composed of nitrogen (78%), oxygen (21%), argon (0.93%), and other gases such as carbon dioxide, neon, helium, and methane.
- These gases have different properties and functions in the atmosphere.

Importance of Air:
- Air is essential for respiration in living organisms. Oxygen is needed for the process of respiration, where it is used to release energy from food.
- Air helps in regulating the Earth's temperature by trapping heat and preventing extreme fluctuations in temperature.
- It plays a crucial role in the water cycle by carrying water vapour and facilitating the process of precipitation.

Properties of Air:
- Air is a mixture of gases that can be compressed, expanded, and exert pressure.
- It has weight and occupies space, which can be demonstrated through experiments like inflating a balloon or using a syringe to show the compressibility of air.

Pollution and Conservation:
- Human activities such as burning fossil fuels, industrial processes, and deforestation have led to air pollution, which can have harmful effects on human health and the environment.
- It is important to take measures to conserve air quality by reducing emissions, promoting clean energy sources, and adopting sustainable practices.
In conclusion, air is a vital component of our environment that sustains life on Earth. Understanding its composition, importance, properties, and the need for conservation is essential for maintaining a healthy and sustainable planet.