The group 14 elements A and B have the first ionisation enthalpy values of 708 and $715\;{\rm{kJ}}\;{\rm{mo}}{{\rm{l}}^{ - 1}}$ respectively. The above values are lowest among their group members. The nature of their ions ${{\rm{A}}^{2 + }}$ and ${{\rm{B}}^{4 + }}$ respectively is