Why is second ionization energy of alkali metals higher than alkaline earth metals?

Explanation

(i) The second ionisation enthalpi es of alkali metals are very high. The removal of an electron from the alkali metals gives monovalent cations having stable electronic configurations similar to the noble gas. Therefore, it becomes very difficult to remove the second electron so has Very high I.E
(ii) In the case of alkaline earth metals, the second electron is to be removed from a monovalent cation, which still has one electron in the outermost shell. Thus, the second electron can be removed more easily in the case of group 2 efernents since it results in the noble gas configuration.