The reaction of chlorine on gain of electron is given as Cl(g)+e−→Cl−(g) It is given the ground state of Cl(g) is xkJmol−1 It is assumed the ground state of Cl−(g) is ykJmol−1 The electron gain enthalpyis given as, ∆egH=Ep−ER −349‌kJ∕mol=y−x y=(x−349)kJ∕mol