Question

The correct order of energy of 2s-orbitals in H, Li, Na and K, is

(a) K < Na < Li < H

(b) Na < Li < K < H

(c) Na < K < H < Li

(d) H < Na < Li < K

Answer 1

Answer is : (a) K < Na < Li < H

As the atomic number increases, the energy of orbital decreases. This is because the atomic radii decreases (nuclear charge increases) with increase in atomic number. The atomic number of H, Li, Na and K respectively, are 1, 3, 11 and 19. Thus, the correct order of energy of 2s-orbitals is

K < Na < Li < H.