The first ionization enthalpy $\left(\mathrm{\Delta H}\right)$ values of the third period elements, $\mathrm{Na},\mathrm{Mg}$ and $\mathrm{Si}$ are respectively $496,737$ and $786{\mathrm{kJmol}}^{-1}$. Predict the first ionization enthalpy $\left(\mathrm{\Delta }H\right)$ value of Al :

The energy required to expel the outermost, or highest energy, electron from a neutral atom in the gas phase is known as an element's initial ionization energy. It is known that the first ionization energy of Al is more than the sodium (737) but it is less than the Mg (496).
So the first ionization energy of Al near 575.

Hence, the option C is correct