Which of the following represents the correct order of increasing electron gain enthalpy with negative sign for the elements $O$,$S$,$F$ and $Cl$?

The formation of the oxide ion,$O^{2-}_{(g)}$ from an oxygen atom requires first an exothermic and then an endothermic step as shown below:
$O_{(g)} + e^- \to O^{-}_{(g)} ; \Delta_f H^o = -141 \ kJ \ mol^{-1}$
$O^{-}_{(g)} + e^- \to O^{2-}_{(g)} ; \Delta_f H^o = +780 \ kJ \ mol^{-1}$
Thus,the process of formation of $O^{2-}$ in the gas phase is unfavourable even though $O^{2-}$ is isoelectronic with neon. This is due to the fact that,

The formation of the $O^{2-}$ ion is first exothermic and then endothermic,as shown by the following reaction steps:
$O_{(g)} + e^- \to O^-_{(g)}; \Delta H^o = -142 \ kJ \ mol^{-1}$
$O^-_{(g)} + e^- \to O^{2-}_{(g)}; \Delta H^o = 844 \ kJ \ mol^{-1}$
This is due to:

The electron affinities of halogens are $F = 322, Cl = 349, Br = 324, I = 295 \ kJ \ mol^{-1}$. The higher value for $Cl$ as compared to that of $F$ is due to :-

The electron gain enthalpy (in $kJ/mol$) of fluorine,chlorine,bromine and iodine,respectively,are:

Which element has the highest electron gain enthalpy?