A colourless gaseous element belonging to group 0 (the noble gases) of the periodic table; a.n. 36; r.a.m. 83.80; d. 3.73 g m−3; m.p. –156.6°C; b.p. –152.3°C. Krypton occurs in air (0.0001% by volume) from which it can be extracted by fractional distillation of liquid air. Usually, the element is not isolated but is used with other inert gases in fluorescent lamps, etc. The element has five natural isotopes (mass numbers 78, 80, 82, 83, 84) and there are five radioactive isotopes (76, 77, 79, 81, 85). Krypton–85 (half-life 10.76 years) is produced in fission reactors and it has been suggested that an equilibrium amount will eventually occur in the atmosphere. The element is practically inert and forms very few compounds (certain fluorides, such as KrF2, have been reported). Krypton was discovered in 1898 by Sir William Ramsay (1852–1916) and Morris Travers (1872–1961).
https://www.webelements.com/krypton/ Information from the WebElements site