The correct option is B Pauli's exclusion principle
Quantum numbers of an atom can be defined on the basis of Pauli's exclusion principle. The Pauli Exclusion Principle states that, in an atom or molecule, no two electrons can have the same four electronic quantum numbers. As an orbital can contain a maximum of only two electrons, the two electrons must have opposing spins. This means if one is assigned an up-spin ( +1/2), the other must be down-spin (-1/2).