In the comics, the planet Colu, on TV the planet Krypton, just like Superman does.

Planet Krypton is a fictional planet in the DC Comics universe and is typically associated with the star system Rao in the Andromeda galaxy.

Supergirl first appeared in Action Comics #252 (May 1959) titled The Supergirl from Krypton

Kryptonite is a fictional material from the Superman comics, not a real element. It does not have a chemical symbol.

Yes, krypton is a real element on the periodic table. It is a noble gas with the atomic number 36 and symbol Kr. Krypton is odorless, colorless, and tasteless, and is used in lighting, lasers, and in some specialized photographic flash lamps.