The correct order of electron gain enthalpy with negative sign of F, Cl, Br and I, having atomic numbers 9, 17, 35 and 53, respectively, is

Amongst halogens, chlorine has the maximum value of electron affinity. This is because fluorine involves more electron-electron repulsion due to more compact electronic configuration causing the electron affinity value less than chlorine. Since the electron gain enthalpy for halogens has negative value (i.e. release of energy), the negative of the electron gain enthalpy will follow the order $\mathrm{Cl}>\mathrm{F}>\mathrm{Br}>\mathrm{I}$.