In the compound cah2 calcium has an oxidation number of 2 + and hydrogen has an oxidation number of

The oxidation number of H is - 1.

Sum of the oxidation numbers in each element = charge of the complex

CaH₂ has 1 Ca atom and 2H atoms. The charge of the complex is zero. Let’s say Oxidation number of H is "a".

Then,

(+2) + 2 x a = 0

+2 + 2a = 0

2a = - 2

a = - 1

Hence, the oxidation number of Hydrogen atom in CaH₂ is - 1