Halogens have maximum negative electron gain enthalpy in the respective periods of the periodic table. Why ?

Explanation

Halogens have the smallest size in their respective periods and therefore have high effective nuclear charge, therefore, they can readily accept one electron to acquire nearest noble gas configuration. As the process is exothermic, halogens have maximum negative electron gain enthalpy (`Delta` e.g. H) in the respective periods.
`underset(ns^2" "np^5)(X(g))+e^(-) overset(Delta H_(eg))to underset(ns^2" "np^6)(X^(-))` (X = F, Cl, Br, I)