a
Elecronic configuration of \(\mathrm{Na}=[\mathrm{Ne}] 3 \mathrm{s}^{1}\)

\({\mathrm{Mg}=[\mathrm{Ne}] 3 \mathrm{s}^{2}}\)

\({\mathrm{Al}=[\mathrm{Ne}] 3 \mathrm{s}^{2} 3 \mathrm{p}^{1}}\)

So order of first ionisation energy is

\(\mathrm{Na}(496)<\mathrm{Mg}(737)>\mathrm{Al}(577)<\text { Si }{(786)}\)

\(\mathrm{Na}<\mathrm{Al}<\mathrm{Mg}<\mathrm{Si}\left(\mathrm{IE}_{1} \text { order }\right)\)