Within each pair of elements F & Cl, S & Se, and Li & Na, respectively, the element that release more energy upon an electron gain are:

(i) Electron affinity of second period p-block element is less than third period p-block element due to small size of second period p-block element.          E.A. order : F < Cl (ii) Down the group electron affinity decreases due to size increases.          EA. Order : S > Se                             Li > Na