Question: which one of the following sets of quantum numbers is not permitted?
Answer: 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. The angular quantum number (l) can be any integer between 0 and n - 1.