No, it's not Kryptonite. Though Superman's writers probably DID get inspiration from the periodic table. The real thing, krypton gas, is an inert element with few major uses other than lighting. The discharge glow is an eerie white compared to counterpart neon's well-known orange. Breathing pure krypton can put you to sleep in a matter of seconds so it could also be used as a safe anesthetic for surgery except it's just too expensive.

A little vial of it in a solid acrylic cube is certainly affordable however and will look great in your elements collection!