First ionisation enthalpy of Magnesium is 738 kJ/mole. The change in enthalpy for the process  $\mathrm{Mg}\left(\mathrm{g}\right) \to {\mathrm{Mg}}^{2+}\left(\mathrm{g}\right)$ will be

Given

I.P₁ of Mg = + 738 kJ/mole ;

I.P₂ of Mg must be > 738 kJ/mole ;

Thus sum of I.P₁ and I.P₂ will be > 1476 kJ

Thus

$\mathrm{Mg}\left(\mathrm{g}\right) \to {\mathrm{Mg}}^{2+}\left(\mathrm{g}\right), ∆\mathrm{H} >1476 \mathrm{kJ} ;$

By inspection, the only option which is greater than 1476 kJ is Option (2)