Aluminium is obtained by the electrolysis of purified bauxite. Which row gives the half-equations at the electrodes and states why one of the electrodes must be replaced regularly?
- AAnode: $2\text{O}^{2-} \rightarrow \text{O}_2 + 4e^-$; Cathode: $\text{Al}^{3+} + 3e^- \rightarrow \text{Al}$; cathode replaced as it gets coated with aluminium
- BAnode: $2\text{O}^{2-} \rightarrow \text{O}_2 + 4e^-$; Cathode: $\text{Al}^{3+} + 3e^- \rightarrow \text{Al}$; anode replaced as it burns away in oxygen
- CAnode: $\text{Al}^{3+} + 3e^- \rightarrow \text{Al}$; Cathode: $2\text{O}^{2-} \rightarrow \text{O}_2 + 4e^-$; cathode replaced as it burns away in oxygen
- DAnode: $\text{Al}^{3+} + 3e^- \rightarrow \text{Al}$; Cathode: $2\text{O}^{2-} \rightarrow \text{O}_2 + 4e^-$; anode replaced as it gets coated with aluminium