MHT CET 2017 Chemistry Solved Paper

(b) Electron gain enthalpy becomes lessnegative on moving from chlorine to iodine.However, negative electron gain enthalpyof fluorine is less than that of chlorine dueto small sized of fluorine atom. It has veryhigh inter electronic repulsion in therelatively small 2p orbitals. Hence, incomingelectron experience less attraction from thenucleus.
∴ Chlorine has the highest value of electrongain enthalpy.