Krypton is a gas with no colour or smell. It does not react with anything except fluorine gas.

Why is krypton so unreactive?

It's not just Superman's home planet; Krypton is one of the rarest gases on Earth, composing only 1 part per million of the atmosphere by volume. This noble gas is colorless and odorless. It has a full outer shell of electrons, rendering it largely inert to reactions with other elements.

Is krypton reactive or radioactive?

Kr is an inert radioactive noble gas with a half-life of 10.76 years. It is produced by the fission of uranium and plutonium, such as in nuclear bomb testing and nuclear reactors.