Oxygen - O, 8

Oxygen gas is colorless, odorless, and tasteless. The liquid and solid forms are a pale blue color and are strongly paramagnetic. Oxygen supports combustion, combines with most elements, and is a component of hundreds of thousands of organic compounds. Ozone (O3), a highly active compound with a name derived from the Greek word for 'I smell', is formed by the action of an electrical discharge or ultraviolet light on oxygen.

Oxygen was the atomic weight standard of comparison for the other elements until 1961 when the International Union of Pure and Applied Chemistry adopted carbon 12 as the new basis. It is the third most abundant element found in the sun and the earth, and it plays a part in the carbon-nitrogen cycle. Excited oxygen yields the bright red and yellow-green colors of the Aurora. Oxygen enrichment of steel blast furnaces accounts for the greatest use of the gas. Large quantities are used in making synthesis gas for ammonia, methanol, and ethylene oxide. It is also used as a bleach, for oxidizing oils, for oxy-acetylene welding, and for determining carbon content of steel and organic compounds. Plants and animals require oxygen for respiration. Hospitals frequently prescribe oxygen for patients. Approximately two thirds of the human body and nine tenths of the mass of water is oxygen.