Krypton is a gas that is present in air at about 1 parts per million. A small amount is also present in the atmosphere of Mars, at about 0.3 ppm.
Krypton is colorless and odorless and os considered a rare gas. It was discovered by boiling away water, nitrogen, oxygen, helium and argon from a sample of liquid air. The Earth's atmosphere as a whole is about 0.0001 percent krypton. Krypton is put to use in some fluorescent light bulbs, airport runway lights, yellow-green luminous signs and flash bulbs for high speed photography. It is also used in a number of different types of lasers.