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

The correct option is B $O<S<F<Cl$
The correct order of electron gain enthalpy (with negative sign) of given atomic species is $O<S<F<Cl$.

In a period, on moving from left to right, electron affinity increases due to increase in the effective nuclear charge and decrease in size.

In a group on moving from top to bottom, the electron affinity decreases due to decrease in the effective nuclear charge and increase in size. But there is an exception for $F$ and $O$ due to its small size.