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

Key Idea:- Electron gain enthalpy, generally, increases in a period from left to right and decreases in a group on moving downwards. However, members of III period have somewhat higher electron gain enthalpy as compared to the corresponding members of second period, because of their small size. $\mathrm{O}$ and $\mathrm{S}$ belong to VI A (16) group and $\mathrm{Cl}$ and $\mathrm{F}$ belong to VII A (17) group. Thus, the electron gain enthalpy of $\mathrm{Cl}$ and $\mathrm{F}$ is higher as compared to $\mathrm{O}$ and $\mathrm{S}$. $\mathrm{Cl}$ and $\mathrm{F}>\mathrm{O}$ and $\mathrm{S}$ Between $\mathrm{Cl}$ and $\mathrm{F}, \mathrm{Cl}$ has higher electron gain enthalpy as in $\mathrm{F}$, the incoming electron experiences a greater force of repulsion because of small size of $\mathrm{F}$ atom. Similar is true in case of $O$ and $S$ ie, the electron gain enthalpy of $S$ is higher as compared to $O$ due to its small size. Thus, the correct order of electron gain enthalpy of given elements is $$ \mathrm{O} < \mathrm{S} < \mathrm{F} < \mathrm{Cl} $$