Which pf the following orbitals are not possible?
`2d,4f,4g` and `6d`

Answer

`2d` is not possible. For d sub-shell `I=2`. When `n=2,I` can be 0 and 1. Since `I` cannot be 2 for `n=2` hence `2d` sub-shell is not possible.
`4f` is possible. For f-sub-shell `I=3`. When `n=4,I` can be equal to 3
`4g` is not possible. For g-sub-shell `I=4. When `n=4, I` cannot be equal to 4.
`6d` is possible. For d-sub-shell `I=2`. When `n=6,I` can be equal to 2.