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

• Cl < F < O < S

• O < S < F< Cl

• F < S < O < Cl

• S < O < Cl < F

B.

O < S < F< Cl

Electron gain enthalpy, generally, increases in a period from left to right and decreases in a group on moving downwards. However, members of III periods have somewhat higher electron gain enthalpy as compared to the corresponding members of the second period because of their small size.
O and S belong to VI A (16) group and Cl and F belong to VII-A (17) group. Thus, the electron gain enthalpy of Cl and F is higher as compared to O and S.
Cl and F > O and S
Between Cl and F, Cl has higher electron gain enthalpy as in F, the incoming electron experiences a greater force of repulsion because of the small size of F atom. Similarly is true is a 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 
O < S < F < Cl