Correct Answer: Spin quantum number

Solution : The correct option is the spin quantum number .

No two electrons in an atom can have the same set of quantum numbers, according to the Pauli Exclusion Principle , which includes the primary quantum number (n), the angular momentum quantum number (l), the magnetic quantum number (m) and the spin quantum number (s). Because an orbital can only accommodate two electrons with opposing spins, the spin quantum number differentiates the two electrons inside the same orbital. One electron will have an upward spin of +1/2, while the other will have a downward spin of -1/2 . This distinction aids in adhering to the idea of electron pairing and contributes to the atom's stability.