Krypton

Definitions

1. The chemical element (symbol Kr) with an atomic number of 36. It is a colourless, odourless noble gas that only reacts with fluorine. It is one of the rarest gases in the Earth's atmosphere.
   uncountable
2. A fictional planet, the native world of Superman, named after the element krypton.
3. An atom of this element.
   countable

Equivalents

CEFR level