Krypton is a chemical element, having the chemical symbol Kr. Its atomic number (the number of protons) is 36. It has a standard atomic weight of 83.798 g•mol −1 and is a gas in its elemental form.
Krypton is a monatomic noble gas. At a pressure of 101.325 kPa, it has a boiling point of −153.22 °C and a melting point of −157.38 °C.
The isotope 85Kr is emitted by the process of producing plutonium, and air sampling for it, as well as for 133Xenon, is used in Materials MASINT and national technical means of verification as a way to remotely monitor such facilities. It is also released by atmospheric nuclear explosions.