The electron gain enthalpy (in kJ m o l ) of fluorine, chlorine, bromine and iodine, respectively, are

Step-by-step solution

Order of electron gain enthalpy Cl > F > Br > I Electron gain enthalpy of third period elements are greater than second period elements. Electron gain enthalpy decrease down to the group, but here Electron gain enthalpy of chlorine is greater than fluorine, it is due to small size of fluorine atom, due to which electron density is high than chlorine, hence upcoming electron face high repulsion in F atom, hence the energy released is less than chlorine.