Brine is electrolysed using inert electrodes. The reaction at the anode is _____.

Brine is a saturated solution of Sodium chloride in water. It contains a substantial amount of chloride(Cl^-) ions compared to hydroxyl (OH^-) ions.

Reduction potential value of Chlorine (Cl₂ + 2e → 2Cl^-) is 1.36V whereas that of Oxygen (O₂+ 2H₂O + 4e → 4OH-) is 0.40V.So O₂ gas should be oxidized at anode instead of Cl₂.

But since the amount of Cl^- ions are much more than OH- ions, so Cl^- ions are preferentially oxidized at the anode to liberate Cl₂ gas.