Nitrogen was discovered by:

Nitrogen was discovered in 1772 by the Scottish physician and chemist Daniel Rutherford (1749-1819), while he was a student at the University of Edinburgh. He was a student of Joseph Black, who had earlier discovered carbon dioxide ("fixed air").

In his experiment, Rutherford burnt substances, such as candles and phosphorus, in a closed container of air, and kept a mouse in it until it died. He then removed the carbon dioxide by passing the remaining air through a solution of potash (an alkali). The gas left over could not support burning or life. He called it "noxious air" or "phlogisticated air", following the phlogiston theory of combustion popular at the time. Around the same time, other scientists, such as Carl Wilhelm Scheele, Henry Cavendish and Joseph Priestley, also studied this gas, but Rutherford is credited with its discovery because he published first.

The French chemist Antoine Lavoisier later recognised it as an element and called it "azote", meaning "without life", because animals could not live in it. The name "nitrogen" was proposed in 1790 by Jean-Antoine Chaptal, from "nitre" (potassium nitrate) and "-gen" (producer), because it is a component of nitre.

Facts about nitrogen:

• It has atomic number 7 and is in Group 15 of the periodic table.
• It makes up about 78% of the Earth's atmosphere by volume, making it the most abundant gas in the air.
• It exists as a diatomic molecule (N2), with a very strong triple bond, which makes it quite unreactive.

It is essential for life, as a component of proteins, DNA and RNA. Plants obtain it through nitrogen fixation by bacteria such as Rhizobium, and through fertilisers such as urea.

Liquid nitrogen, boiling at –196°C, is used to preserve biological samples and in cryosurgery.

Why not the other options?

• ✗Joseph Priestley discovered oxygen in 1774 (independently of Scheele).
• ✗Henry Cavendish discovered hydrogen in 1766.
• ✗Antoine Lavoisier named oxygen and hydrogen and showed the role of oxygen in burning.