The orbital quantum number, l, divides the shells up into smaller groups of subshells called orbitals. The orbital quantum number describes shape of subshells. The principal quantum number(n) determines the possible values of l. For n=1 i.e. K-shell there is no subshell so, l=0 i.e. (n−1). Hence, The possible values of orbital quantum numbers are from 0 to (n−1).