Molecular hydrogen is produced as a byproduct in the industrial production of NaOH by electrolysis of aq NaCl solution NaCl→Na++Cl− H2O⇌H++OH− Cathode : 2H2O+2e→H2+2OH− Anode :2Cl−→Cl2+2e NaOH is crystallised from the remaining part of electrolyte.