A beaker containing aqueous Li+, Na+ and K+ ions are electrolysed. Reaction taking place at cathode is , M+(aq)+e−⟶MCations are discharged at the cathode in the order

K+(first ),Na+,Li+Smaller the size of the cation, larger the charge on the cation, then larger the hydration and hydration energy and larger the size of the hydrated ion. ion becomes heavier and ionic velocity is retarded when electric field is applied.