Impossible orbital among the following is

According to Bohr - Burry's scheme, Maximum number of $\mathrm{e}^{-}$in 3 rd orbital $=3 \mathrm{n}^{2}$ $$ =3(3)^{2}=18 $$ and maximum number of $\mathrm{e}^{-}$in s-subshell $=2$ p-subshell $=6$ d-subshell $=10$ f-subshell $=14$ Therefore, $18 \mathrm{e}^{-}$present in 3rd orbital enter in s, $\mathrm{p}$ and $\mathrm{d}$ subshell. Thereafter, there is no $\mathrm{e}^{-}$ available for f-subshell. That's why $3 \mathrm{f}$ subshell is not possible.