Question

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

(1) F, Se and Na 

(2) F, S and Li 

(3) Cl, S and Li 

(4) Cl, Se and Na

Answer 1

Answer is (3) Cl, S and Li

(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

Answer 2

Answer is (3) Cl, S and Li