Redox Roles in Halogen Displacement

Steps:

• Assign oxidation numbers: Cl in Cl₂ is 0, in KCl is -1; Br in KBr is -1, in Br₂ is 0.
• Chlorine decreases from 0 to -1 (gains electrons, reduced).
• Bromine increases from -1 to 0 (loses electrons, oxidized).
• Oxidizing agent is the reduced species (Cl₂); reducing agent is the oxidized species (Br⁻).

Why D is correct:

• Chlorine (Cl₂) is reduced (oxidation number decreases), oxidizing Br⁻ per the definition of oxidizing agent as the electron acceptor.

Why the others are wrong:

• A: Bromine (Br₂) is the oxidized product, not reduced, so not oxidizing agent.
• B: Bromine (Br₂) is the result of oxidation; reducing agent is Br⁻ from KBr.
• C: Chlorine (Cl₂) is reduced, not oxidized, so not reducing agent.

Final answer: D