Among halogens, the correct order of amount of energy released in electron gain 3 (electron gain enthalpy) is:
(i) F > Cl > Br > I
(ii) F < Cl < Br < I
(iii) F < Cl > Br > I
(iv) F < Cl < Br < I
The answer is the option (iii) F < Cl > Br > I
Explanation: Within the same group, electron gain enthalpy becomes less negative while going down in the group. However, with the addition of an electron to the 2p-orbital leads to greater repulsion than the addition of an electron to the larger 3p- orbital. Hence, in following halogens, chlorine is the element with the highest negative electron gain enthalpy.