Question

Is (kr) an element a compound or a mixture?

Answer 1

Krypton ... symbol Kr ... is an element.  It's element number 36, because
there are 36 protons in the nucleus of every atom of Krypton. 

Krypton has nothing to do with Superman, except that about 75 years ago,
the creators of Superman thought it was a cool-sounding scientific word,
so they chose it for the name of his home planet.

Answer 2

I believe it is a compound of a mixture or or mixture