Answer: HCl, because the oxidation number of Cl changes from -1 to 0.
Step-by-step explanation:
This reaction is considered as oxidation-reduction reaction that contain a reducing and oxidizing agent in the reactants.
The reducing agent is the agent that is oxidized and loss electrons and reduce the other agent.
The oxidizing agent is the agent that is reduced and gain electrons and oxidize the other agent.
- First choice is wrong because the oxidizing agent is KMnO4, that its oxidation number changes from +7 to +2 and gain 5 electrons (reduction occur to KMnO4).
- The second choice is wrong because the oxidation state of K remain the same (+1) and do not change.
- The third choice is wrong because the oxidation state of H remain the same (+1) and do not change.
- The fourth choice is the right answer because HCl is the reducing agent that oxidized to Cl2 and the oxidation state changes from (-1) to (0) and reduce the KMnO4.