Mixture containing aqueous Li+, Na+,K+ ions are electrolysed. Cations are discharged at cathode in the order M+(aq)+e−⟶M

Greater the hydration, smaller the ionic mobility of cation to move towards cathode, Li+ is heavily hydrated, thus has least ionic mobility and these discharged at the end. K+ is least hydrated, then, has maximum ionic mobility and discharged first.