What is the purpose of nitrogen in the air ?

in the atmosphere it helps to reduce the effect of O₂ by controlling the rate of combustion,oxidation and corrosion of metal.

Nitrogen is a big part of Earth’s atmosphere. In fact, nitrogen makes up 78 percent of our air. Nitrogen is extremely important in living things. It forms the building blocks of proteins. We need proteins because they make up our skin and hair. Proteins also help us digest food. We get our nitrogen from plants, and plants get it from bacteria in the soil. Our atmosphere provides life with the nitrogen it needs.