Question

Explain why the quantum number set (2, 2, -1, -½) is not possible for an electron in an atom.

Answer 1

this is becoz when n=2 then l=n-1=1

Answer 2

because 2nd shell does not have d sub shell.

subsidary quantum no, l = (n-1) [where n is principal quantum no]

so, n can never be equal to l.