Question: which one of the following combinations of quantum numbers is not allowed?
Answer: Rules Governing the Allowed Combinations of Quantum Numbers The three quantum numbers (n, l, and m) that describe an orbital are integers: 0, 1, 2, 3, and so on. The principal quantum number (n) cannot be zero. The allowed values of n are therefore 1, 2, 3, 4, and so on.