Answer: c) H2 + Cl2 → 2HCl
Explanation:
a) is a wrong answer because it is a dissociation reaction that H2 dissociated to its H atoms and have the same oxidation state (0).
b) Also, a wrong choice that oxygen have the same oxidation state (-1).
c) is the right answer that the oxidation state is changed for both H and Cl, that H2 is oxidized and its oxidation state changed from 0 to +1 (loss of electrons). On the other hand, Cl2 is reduced that its oxidation state changed from 0 to -1 (gain of electrons). So, this reaction is considered as an oxidation-reduction reaction.
d) is a replacement reaction without changing the oxidation state or reactants and products so it is a wrong answer.
