We know that the electron gain enthalpy increases from left to right and decreases from top to bottom. So here, Fluorine has maximum electron gain enthalpy. Now in $2^{\mathrm{nd}}$ period size of elements are too small so inter-electronic repulsion is maximum and due to this reason it is slightly difficult to add the electron in elements of $2^{\mathrm{nd}}$ group therefore after fluorine sulphur have higher electron gain enthalpy. Hence, the final order will be:

$\mathrm{F}>\mathrm{S}>\mathrm{O}>\mathrm{N}$