Aluminium may be extracted by electrolysing aluminium oxide dissolved in molten cryolite. Which reactions occur during this electrolysis?
- Areaction at the anode: $\text{Al}^+ + e^- \rightarrow \text{Al}$; reaction at the cathode: $\text{O}^{2-} + 2e^- \rightarrow \text{O}$
- Breaction at the anode: $\text{Al}^{3+} + 3e^- \rightarrow \text{Al}$; reaction at the cathode: $2\text{O}^{2-} + 4e^- \rightarrow \text{O}_2$
- Creaction at the anode: $\text{O}^{2-} - 2e^- \rightarrow \text{O}$; reaction at the cathode: $3\text{Al}^{3+} + 3e^- \rightarrow 3\text{Al}$
- Dreaction at the anode: $2\text{O}^{2-} - 4e^- \rightarrow \text{O}_2$; reaction at the cathode: $\text{Al}^{3+} + 3e^- \rightarrow \text{Al}$