The half-reaction Al3+ + 3e- → Al occurs at which electrode?

• A. Anode
• B. Cathode
• C. Both
• D. None

Answer: (B)

Reduction is the process of gaining electrons. In the given half-reaction, Al3+ gains three electrons to become Al, so this reaction occurs at the electrode where reduction takes place—the cathode. The cathode is the site where electrons are supplied to ions, allowing reduction to happen. The opposite electrode is the anode, where oxidation would occur (Al metal would lose electrons to form Al3+). Whether the cell is galvanic or electrolytic, reduction always happens at the cathode, so this reaction takes place there.