Answer:- C. H
Explanations:- Reduction is gain of electron. In other words we could say that decrease in oxidation number is reduction.
As per the rules, oxidation number of hydrogen in its compounds is +1(except metal hydrides) and the oxidation number of oxygen in its compounds is -2.
The oxidation number in elemental form is zero.
In , the oxidation number of H is +1 and oxidation number of O is -2. Oxidation number of Cl in
is -1. On product side, the oxidation number of hydrogen in
is zero and in
the oxidation number of H is +1 and that of O is -2. Oxidation number of Cl in
is 0.
From above data, Oxidation number of O is -2 on both sides so it is not reduced.
Oxidation number of Cl is changing from -1 to 0 which is oxidation.
Oxidation number of H is changing from +1 to 0 which is reduction.
So, the right choice is C.H