Electron affinity increases along the period from left to right and is decreases as we move down the group. The values of electron affinity for the given species are as follows: S ( sulphur ) =200kJ∕mol Se (selenium) =195kJ∕mol O ( oxygen ) =141.1kJ∕mol Hence, correct order is : S>Se>O, but as electron affinity of S≈ Se, we can also write it as Se>S>O and option (c) will be the correct answer. Note Electron affinity of S>O, due to very small size of oxygen having lone pair of electrons, which offer more repulsion for the incoming electron.