Question

If $(n+l)=6$, then what will be the possible number of the sub-shells?

Answer 1

It is given that, the value of $n+l=6$,
then $n+l=6$
$6+0=6$
$5+1=6$
$4+2=6$

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
$\begin{array}{c}3+3=6\\ 2+4=6\\ 1+5=6\\ 0+6=6\end{array}|$ Not Possible
$3+3$ not possible as value $l=(n-1)$.

Hence total number of sub-shells would be $3$.