It is given that, the value of n + l = 6,
then n + 1 = 6
6 + 0 = 6
5 + 1 = 6
4 + 2 = 6
All above can be possible as values of ‘n’ are greater than the values of ‘l’. But, if the values of n are less than l, then other combination would be
3 + 3 not possible as value of l = (n – 1 ). Hence total number of sub-shells would be 3.