What is a Kryptonite?

Answer:
In Superman comics, one of the few things that can defeat Superman is a strange metal called Kryptonite that comes from the planet Krypton. Although the gas krypton exists in air, kryptonite does NOT.
First answer by Sandyy11. Last edit by Ratbastid. Contributor trust: 2 [recommend contributor recommended]. Question popularity: 1 [recommend question].