Aqueous sodium chloride solution is electrolysed when it is concentrated. Which equation shows the reaction occurring at the cathode?
- A$\text{Na}^+ + e^- \rightarrow \text{Na}$
- B$2\text{O}^{2-} \rightarrow \text{O}_2 + 4e^-$
- C$2\text{H}^+ + 2e^- \rightarrow \text{H}_2$
- D$2\text{Cl}^- \rightarrow \text{Cl}_2 + 2e^-$