Anode Consumption in Hall-Héroult Process

Steps:

• Electrolysis of Al2O3 uses carbon electrodes in molten cryolite.
• At cathode: Al³⁺ + 3e⁻ → Al (aluminum metal deposits).
• At anode: 2O²⁻ → O₂ + 4e⁻ (oxygen gas forms).
• Oxygen reacts with carbon anode: 2C + O₂ → 2CO₂, eroding the anode.

Why A is correct:

• Oxygen gas from anode oxidation reacts directly with the carbon anode, forming CO₂ and consuming the electrode per the redox reaction.

Why the others are wrong:

• B: Oxygen at anode does not reach or react with the cathode.
• C: Aluminum metal at cathode does not migrate to or react with the anode.
• D: Aluminum deposits on the cathode without self-reaction.

Final answer: A