Explanation

(b)
The energy liberated when an electron is added to an isolated gaseous atom is called electron affinity. Thus, as the size increase lesser energy is liberated and hence electron affinity decrease .But the electron affinity of Cl is higher than the electron affinity of F although F has smaller size. This is because the imcoming electron, in case of F experience a greater force of repulsion from the outer electrons of F. Thus to overcome the repulsion some relased energy is utilized . Hence lesser energy is released. Thus the electron affinity is highest for Cl.