∵ First ionisation enthalpy for 1 mole of Mg =737.76J∕mol−1 and second ionisation enthalpy for 1 mole of Mg =1450.73J∕mole−1 Total energy required =737.76+1450.73 =2188.49J∕mole−1 Also, 24g‌of‌Mg=1‌mole‌of‌Mg ∴ Energy required =2188.49J=2.188‌kJ