In the electrolysis of molten sodium iodide, which species is oxidized at the anode?

• A. Na+ -> Na(s)
• B. I2 -> I-
• C. Cu -> Cu2+ + 2 e-
• D. I- -> I2

Answer: (D)

At the anode, oxidation occurs. In molten NaI, the only species available to be oxidized are the iodide ions. They lose electrons to form diatomic iodine: 2 I− → I2 + 2 e−. This is the oxidation happening at the anode, which is why iodide becomes iodine.

Other possibilities would require reducing the cation at the cathode (Na+ to Na) or involve reactions that aren’t available in this molten-salt system (I2 gaining electrons to form I− is reduction, not oxidation). Since the question asks what is oxidized at the anode, iodide to iodine is the correct description.