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
