How will you explain that alkali metals are strong reducing agents?

Lower the ionisation enthalpy, greater is the tendency of an element to lose electrons and hence stronger is the reducing character or higher is the reactivity of the element. Since the ionisation enthalpies of alkali metals decrease down the group, therefore, their reducing character or reactivity in the gaseous state increases from Li to Cs i.e. Li < Na < K < Rb < Cs. However, in the aqueous solution, it has been absorbed that the reducing character of alkali metals follows the sequence Na < K < Rb < Cs < Li. In other words, lithium is the strongest reducing agent in aqueous solution.