Liquid nitrogen
Nitrogen is a chemical element with symbol N and atomic number 7. It is the lightest pnictogen and at room temperature, it is a colorless and odorless diatomic gas. Nitrogen is a common element in the universe, estimated at about seventh in total abundance in our galaxy and fifth in abundance in the Solar System. On Earth, the element forms about 78% of Earth's atmosphere and as such is the most abundant pure element. The element nitrogen was discovered as a separable component of air, by Scottish physician Daniel Rutherford, in 1772.
Nitrogen, along with carbon and oxygen, are intermediates in the CNO cycle, one of the two main processes by which main sequence stars fuse hydrogen into helium. This process accounts for only a few percent of the sun's total energy output, but it becomes the dominant process in stars with more than about 1.5 times the sun's mass. Nitrogen is more common in the solar system than in the galaxy as a whole because the solar system is a relatively new galactic feature.
Many industrially important compounds, such as ammonia, nitric acid, organic nitrates (propellants and explosives), and cyanides, contain nitrogen. The extremely strong triple bond in elemental nitrogen (N≡N) dominates nitrogen chemistry, causing difficulty for both organisms and industry in converting the N2 into useful compounds, but at the same time causing release of large amounts of often useful energy when the compounds burn, explode, or decay back into nitrogen gas. Synthetically-produced ammonia and nitrates are key industrial fertilizers and fertilizer nitrates are key pollutants in causing the eutrophication of water systems. Outside their major uses as fertilizers and energy-stores, nitrogen compounds are versatile organics. Nitrogen is part of materials as diverse as Kevlar fabric and cyanoacrylate "super" glue. Nitrogen is a constituent of molecules in every major pharmacological drug class, including the antibiotics. Many drugs are mimics or prodrugs of natural nitrogen-containing signal molecules: for example, the organic nitrates nitroglycerin and nitroprusside control blood pressure by being metabolized to natural nitric oxide. Plant alkaloids (often defense chemicals) contain nitrogen by definition, and thus many notable nitrogen-containing drugs, such as caffeine and morphine are either alkaloids or synthetic mimics that act (as many plant alkaloids do) upon receptors of animal neurotransmitters (for example, synthetic amphetamines).
The role of nitrogen in biochemistry is best summed up by the abbreviation CHON. Living things are made of carbon, hydrogen, oxygen, and nitrogen. Other elements may be important, even essential; but those four elements predominate.