The CORRECT order of first ionisation enthalpy is:

The ionization energy of the elements increases from left to right in the periodic table. The first ionization of magnesium is greater than that of aluminium because magnesium has a stable complete electronic configuration $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^2$, so it requires more energy to remove the first electron from it, whereas aluminium has electronic configuration $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^1$ which need lesser energy than that of magnesium. Similarly, phosphorus has more ionisation energy than sulphur due to the half filled electronic configuration in the phosphorus.

$\mathrm{Mg} \mathrm{Al} \mathrm{P} \mathrm{S}\to \mathrm{IE} .\mathrm{order} \Rightarrow \mathrm{Al}<\mathrm{Mg}<\mathrm{S}<\mathrm{P}$