Question

in which of the following reaction di hydrogen acts as an oxidising agent

Answer 1

In the first reaction hydrogen is acting as an oxidising agent. This is so as it itself is getting reduced and helping Ca to get oxidised. Reduction is gain of electrons and oxidation is loss of electrons. In the 1st reaction. Ca is losing electrons to provide it to hydrogen and hydrogen gains the electrons lost by Ca. Hence, they form an ionic bond and form CaH2.