Which one of the following arrangements represents the correct order of electron gain enthalpy (with negative sign) of the given atomic species

The correct answer is:

Halogens have very high electron affinities. It may be noted that the electron affinity of fluorine is unexpectedly low . This may perhaps be due to the small size of the F atom. The values of electron gain enthalpies for Cl,F, S and O are respectively 349, 333, 200 and 142 kJ/mole hence correct order is Cl>F>S>O.