Write a balanced half-reaction describing the oxidation of gaseous dihydrogen to aqueous hydrogen cations.

The oxidation state of hydrogen gas is 0 and oxidation state of hydrogen cation is + 1.

There’s an increase in oxidation number therefore it’s an oxidation reaction.

Oxidation reactions give out electrons. The masses and charges on both sides should be balanced

Half reaction is

H2 - > 2H + + 2e