The first ionization energy

All given elements belongs to period III and generally their ionisation energy will increase along the period but Mg will show higher ionisation potential compared to $\mathrm{Al}$ due to its stable configuration. Thus correct order of ionisation energy will be : $\mathrm{Na}<\mathrm{Al}<$ $\mathrm{Mg}<$ Si.

Ionisation energy $(\mathrm{kJ} / \mathrm{mol})$ of the given metals are $\mathrm{Na}: 496 ; \mathrm{Al}: 577 ; \mathrm{Mg}: 737 ; \mathrm{Si}: 786$