A concentrated aqueous magnesium bromide solution is electrolysed with carbon electrodes. Which equations show the reactions taking place at each electrode?
- Apositive: $2\text{Br}^-\text{(aq)} \rightarrow \text{Br}_2\text{(aq)} + 2e^-;\ \text{negative: } 2\text{H}^+\text{(aq)} + 2e^- \rightarrow \text{H}_2\text{(g)}$
- Bpositive: $2\text{H}^+\text{(aq)} + 2e^- \rightarrow \text{H}_2\text{(g)};\ \text{negative: } 2\text{O}^{2-}\text{(aq)} \rightarrow \text{O}_2\text{(aq)} + 4e^-$
- Cpositive: $\text{Mg}^{2+}\text{(aq)} + 2e^- \rightarrow \text{Mg(s)};\ \text{negative: } 2\text{Br}^-\text{(aq)} \rightarrow \text{Br}_2\text{(aq)} + 2e^-$
- Dpositive: $2\text{O}^{2-}\text{(aq)} \rightarrow \text{O}_2\text{(aq)} + 4e^-;\ \text{negative: } \text{Mg}^{2+}\text{(aq)} + 2e^- \rightarrow \text{Mg(s)}$