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 the lowest to highest, as
(iv) < (ii) < (iii) < (i)
(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 Aufbau principle, energies of above mentioned orbitals are in the order of
(iv) 3p < (ii) 4s < (iii) 3d < (i) 4p