Electron gain enthalpy becomes less negative on moving down a group due to increase in atomic size. However, the electron gain enthalpy of F is less negative than Cl due to electron-electron repulsion in small-sized F atom. Thus, the correct order is F<Cl>Br>1. F,Cl,Br and I have ∆egH values (in kJmol−1 ) −328,−349,−325 and −295 respectively. That order of arrangement does not agree with the variation of property.