An exothermic reaction is a chemical reaction where heat is emitted/given off

absorbed/taken in

Emitted/given off. exo is a way to remember that is is going away. think of a flame. the heat is emitted off onto you.

No because it is a noble gas it would need to be put with an alkiline metal become even remotely toxic in any way. Because it krypton being in the noble gases it has only 1 electron and as you might know Alinline metals have 7 and every element wants to have 8. so by putting 7 and 1 together you get 8.