During the industrial extraction of aluminium, molten aluminium oxide, Al2O3\text{Al}_2\text{O}_3Al2O3, is electrolysed.
Which of the following shows the correct half-equations for the reactions occurring at each electrode?
Cathode: Al3+→Al+3e−\text{Al}^{3+} \rightarrow \text{Al} + 3\text{e}^-Al3+→Al+3e− ; Anode: 2O2−→O2+4e−2\text{O}^{2-} \rightarrow \text{O}_2 + 4\text{e}^-2O2−→O2+4e−
Cathode: Al3++3e−→Al\text{Al}^{3+} + 3\text{e}^- \rightarrow \text{Al}Al3++3e−→Al ; Anode: O2−→O2+2e−\text{O}^{2-} \rightarrow \text{O}_2 + 2\text{e}^-O2−→O2+2e−
Cathode: Al3++3e−→Al\text{Al}^{3+} + 3\text{e}^- \rightarrow \text{Al}Al3++3e−→Al ; Anode: 2O2−→O2+4e−2\text{O}^{2-} \rightarrow \text{O}_2 + 4\text{e}^-2O2−→O2+4e−
Cathode: Al3+→Al+3e−\text{Al}^{3+} \rightarrow \text{Al} + 3\text{e}^-Al3+→Al+3e− ; Anode: 2O2−+4e−→O22\text{O}^{2-} + 4\text{e}^- \rightarrow \text{O}_22O2−+4e−→O2