When n = 6, l = 0,1, 2, 3, 4, 5. The order in which the energy of the orbitals increases is 6s < 4f < 5d < 6p. The total number of orbitals available are 16 [s = 1, p = 3, d = 5; / = 7]. The maximum number of electrons which an orbtial can contain is 2. Therefore the sixth period can accomodate 32 elements.
On the basis of quantum numbers, justify that the sixth period of the periodic table should have 32 elements