Answer:
[tex]{ \underline{ \sf{O _{2} \: is \: reduced}}}[/tex]
Explanation:
Reduction means when a reactant loses oxygen or gains hydrogen.
In the equation:
Hydrogen molecule, it neither gains nor loses hydrogen, but it gains oxygen. so :
[tex]{ \sf{H _{2} \: is \: excluded}}[/tex]
Oxygen molecule loses one oxygen atom, and gains four hydrogen atoms, hence it is reduced.
