The electrons identified by quantum numbers n and l (i) n = 4, l = 1 (ii) n = 4, l = 0 (iii) n =3, l = 2 (iv) n = 3, l = 1 can be placed in order of increasing energy, from lowest to highest as

The greater is the value of (n+l), the greater is the energy of orbitals.

(i) n=4,l=1⇒ 4p orbital

(ii) n=4,l=0⇒ 4s orbital

(iii) n=3,l=2⇒ 3d orbital

(iv) n=3,l=1⇒3p orbital

According to the Aufbau principle, energies of above-mentioned orbitals are in the order of-

The increasing order of energy (iv)3p < (ii)4s < (iii)3d < (i)4p