Answer:

i) O and F are from the same period. As the electron is inserted in the same shell, the atomic size of O-atom is larger than F-atom. It has one less proton than F-atom. So an O-atom nucleus cannot attract an electron as strongly as an F-atom nucleus. Also, an F-atom takes just one electron to form a stable inert gas. So, F(fluorine) has a lower electron affinity than O. (oxygen).

(ii) F and Cl are in the same periodic group. The electron affinity decreases as you move along the group. F’s electron affinity is less negative than Cl’s. Because Cl’s atomic size is greater than F’s. The electron will be added to the n = 3 quantum level in Cl and the n = 2 quantum level in F. Adding an electron to Cl is easy because the electron-electron repulsion is minimized. So, Cl has a lower electron affinity than F.