First ionisation enthalpy of Magnesium is 738 kJ/mole. The change in enthalpy for the process  Mgg → Mg2+(g) will be

GivenI.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 kJThusMgg →Mg2+g, ∆H >1476 kJ ;By inspection, the only option which is greater than 1476 kJ is Option (2)