Electron gain enthalphy is the amount of energy involved when an isolated gaseous atom accepts an electron to form a monovalent anion
the value of the electron gain enthalpy of halogens are given below:
F : `-328 KJ mol^(-1) Cl - 349 KJ mol^(-1) Br : -325 KJ mol^(-1) I : -295 KJ mol^(-1)Chlorine has more negative electron gain enthalpy than fluorine. why ?

Explanation

Fluorine atom is smaller in size than chlorine atom. In fluorine atom, added electron goes to the relativity smaller 2p orbital