What is a possible quantum number set for an electron in the 3s orbital of a magnesium atom

There are four quantum numbers in an electron that orbits the atom.

n is a positive integer. The value of n indicates the main shell of the electron. The electron in question is in the 3s orbital. As a result, n = 3.

l is a non-negative integer. The value of l indicates the type of subshell ("orbital") of the electron. The types of subshells possible depends on the main shell. For example, both s and p orbitals exist in the second main shell. However, only the s orbital exists in the first main shell. The value of l ranges from 0 to n - 1.

The electron in question is in an s orbital. As a result, l = 0.

is an integer. The value of indicates the position of the electron within the subshell. The range of depends on the value of l. ranges from -l to l (that's -l, ..., -1, 0, 1, ... l). Accordingly, there are 2 l  + 1 orbitals in a l subshell. l = 0 for this 3s electron. There's only one orbital in the 3s subshell. The only value possible for this electron is 0.

The value of is either - 1/2 or 1/2. It indicates the position of an electron within a single orbital. The value of does not depend on that of n, l, or . However, by the Pauli Exclusion Principle, at least one of the four numbers must differ for two electrons in the same atom. In case all three of n, l, and are the same, the two electrons must differ in . However, this question asks only for the number of one single electron. Thus, giving either - 1/2 or 1/2 shall work.

Vitz et. al, "5.8 Quantum Numbers (Electronic)",  ChemPRIME (Moore et al.), Chemistry Libretexts. 27 Oct 2017.

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