Krypton

Krypton is a colorless, odorless noble gas that rarely reacts with other elements. It occurs in Earth's atmosphere at only about one part per million. Industry obtains it by cooling air into a liquid and separating its components according to their different boiling points, a process called fractional distillation. When an electric discharge passes through krypton gas, it produces a whitish glow, making it useful in some photographic flash lamps. Krypton can also fill the space between window panes to help insulate buildings. Although it is very unreactive, it can form a compound with fluorine under special conditions—a reminder that noble gases are not completely unable to react.