For a hypothetical process , X-(g)→X(g)→X+(g) ; ∆H =+900 KJ,  If Ionization potential of  X-(g) is 150KJ/mole. Then the Electron gain enthalpy of  X+(g) will be

X-(g)→(I)∆IEH=+150KJX(g)→(II)∆H=?X+(g)  ; (II) is IP of X(g) which is endothermic           ∆H = ∆H1+∆H2            900KJ = 150KJ + ∆H2                 ∆H2 = +750KJ/moleMagnitude of  ∆egH of  X+(g) will be the same but will have opposite sign∴ X+(g) +e-→X(g) ; ∆egH = -750KJ