Oxygen (O),
nonmetallic chemical element of Group 16 (VIa, or the oxygen
group) of the periodic table. Oxygen is a colourless, odourless, tasteless gas
essential to living organisms, being taken up by animals, which convert it to carbon
dioxide; plants, in turn, utilize carbon dioxide as a source of carbon and return the
oxygen to the atmosphere. Oxygen forms compounds by reaction with practically
any other element, as well as by reactions that displace elements from their
combinations with each other; in many cases, these processes are accompanied by
the evolution of heat and light and in such cases are called combustions. Its most
important compound is water.