The increasing order of electron affinity of the electronic configurations of element is : (I) 1s22s22p63s23p5                         (II) 1s22s22p3 (III) 1s22s22p5                                   (IV) 1s22s22p63s1

Electron affinity of third period elements is greater than electron affinity of second period elements in the respective group except alkali and alkaline earth metals.Energy is required in adding an electron in nitrogen having half-filled electronic configuration.N < Na < F < Cl.