b
(b) \(I.E.(II)\) of \(Na\) is higher than that of \(Mg\) because in case of \(Na\), the second \({e^ - }\) has to be remove from the noble gas core while in case of \(Mg\) removal of second \({e^ - }\) gives a noble gas core.
\(Mg\) has high first ionisation potential than \(Na\) because of its stable \(n{s^2}\) configuration.