The standard electrode potential of M ^ + / M in aqueous solution...

The stability of ${M}^{+}$ ions in aqueous medium depends on three factors: (i) Enthalpy of atomisation (ii) First ionisation enthalpies of isolated gaseous atom (iii) Hydration enthalpy.

An element in ${M}^{+}$ state in aqueous medium is stabler if the electrode potential ( ${M}^{+} / M$) value of more negative. Down the group, the tendency to form ${M}^{+}$ ion increases. In this process, ionisation of solid metal is not involved in this process.