Nitrogen is the major constituent of air. Air is composed of 78% Nitrogen. Nitrogen serves as diluent as it aids to slow down combustion and corrosion. Without Nitrogen, a match stick been ignited can cause a terrible fire and metals will also corrode easily.

Although Chemically inert, it combines with electropositive metals to form nitrides and with oxygen to form oxides. It is also present in proteins.

Air is composed of about 0.03% by volume of carbon (IV) oxide. It is released into the atmosphere during combustion of hydrocarbons. It is involved in two major processes: Respiration and photosynthesis.

Respiration is the oxidative breakdown of food particles to produce energy. It is a catabolic process (breaking down). $$ C_6H_{12}O_6 + 6O_2 \rightarrow 6H_2O + 6CO_2 $$

Photosynthesis is an anabolic process (building up) which involves the production of food by green plants in the presence of sunlight. $$ 6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2 $$

Noble gases are chemically inert gases. They constitute about 1% by volume of air. They include helium, neon, argon, krypton, xenon and radon. Argon and neon are the most abundant noble gases and are heavier than nitrogen.

1. Helium, being non-combustible is preferred over hydrogen for the filling of balloons due to its low density (almost as light as hydrogen).
2. Argon is used in gas filled lamps because it helps to prevent the oxidation of the lamp filaments.
3. A mixture of krypton and xenon is used in photographer's flash for taking high speed pictures.
4. Radon which is radioactive is used in medicine for the treatment of cancer.
5. Neon light is used in aerodrome due to its high fog penetration power.
6. Helium, neon and Argon are used in advertisement boards. This is because they give out colored light, when a high voltage current is passed through them under low pressure.

The presence of water vapour in the atmosphere is due to evaporation from water bodies. The presence of water vapor can be detected using a deliquescent substance or drying agent e.g calcium chloride. The quantity of water vapor in the atmosphere varies and depends on the rate of evaporation.

Air is sparingly soluble in water, dissolving more in cold water than in hot water. Due to the exposure to the atmosphere, their surfaces contain dissolved air. Oxygen and carbon (IV) oxide are essential for respiration and photosynthesis respectively.