Discovered in 1772, nitrogen is one of the most abundant elements. Every breath that you inhale is nearly 80% nitrogen. It is a colourless, odorless, tasteless, and generally inert gas. Close to 25 million tons of nitrogen are recovered commercially each year from liquefied air by means of a process known as fractional distillation. Nitrogen liquefies at -196 ^oC. As a liquid, it is also colorless and odorless, resembling ordinary water in appearance, density and viscosity.

Nitrogen is of economic importance. Commercially produced nitrogen is used in the following applications:

1. Production of ammonia by the Haber process.
2. Conversion to nitric acid, HNO₃, a primary component in making ammonium nitrate, which is widely used in making explosives. .
3. In an oilfield operation called "enhanced oil recovery", where compressed gas is used to force oil from its underground deposits. Nitrogen is the choice gas for this process because of its unreactivity with the oil.
4. In industrial soldering and welding operations where it is important to keep other atmospheric gases away from the high-temperature part of the work.
5. Production of fertilizers as nitrogen compounds are essential for plant growth.
   • Liquid ammonia is injected directly into the soil for certain crops such as corn and sugar beets.
   • Ammonium sulfate is manufactured because of its widespread use as a fertilizer. Its only drawback as a fertilizer is that it tends to leave an acidic residue in the soil.
   • Ammonium nitrate, because of its high nitrogen content, it is also used as a fertilizer.
   • Urea is another nitrogen-containing compound that is used as a fertilizer. It is also a protein supplement in cattle feed.
6. Dinitrogen oxide, N₂, is used as a mild anaesthetic in medicine and dentistry. It is sometimes called laughing gas because it induces a feeling of elation.
7. Urea is used in the manufacture of urea-formaldehyde resins.

Our body synthesizes nitrogen-containing compounds called amino acids. Various proteins are assembled from the necessary amino acids and it is important that all the amino acids should be present in sufficient quantities. We synthesize 12 of the 20 amino acids in our bodies. The remaining 8 cannot be synthesized by the body and have to be supplied in the diet.