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Which of the following half-reactions can occur at the anode?

1. 2Cr3+ + 7H2O -> Cr2O7²- + 14 H+
2. F2 -> 2 F-
3. 1/2 O2 + 2H+ -> H2O
4. None of these

Correct answer: 2Cr3+ + 7H2O -> Cr2O7²- + 14 H+

Solution

At the anode oxidation occurs; Cr goes from +3 to +6 in this reaction, so it is an oxidation suitable for the anode, while the other two are reductions.

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