7. Chlorine, hydrogen and sodium hydroxide are made by the electrolysis of concentrated aqueous sodium chloride. Aqueous sodium chloride contains the following ions, Na+, H+, OH– and Cl–. Concentrated aqueous sodium chloride can be electrolysed using inert electrodes. The electrode reactions are represented below. Cathode: 2H+ + 2e– à H2 Anode: 2Cl– à Cl2 + 2e– a) Explain why hydrogen, not sodium, is formed at the cathode.  b) Suggest why, as the electrolysis proceeds, the concentration of sodium hydroxide in the electrolyte increases.