WAEC Chemistry 2017 Paper

Concept:The Pauli exclusion principle describes a fundamental rule about how electrons are described by quantum numbers.Explanation:This principle states that no two electrons in an atom can have the same set of all four quantum numbers.The four quantum numbers are the principal quantum number $n$, azimuthal quantum number $l$, magnetic quantum number $m_l$, and spin quantum number $m_s$.When two electrons occupy the same orbital, their values of $n$, $l$, and $m_l$ are identical.Therefore, they must differ in their spin quantum number $m_s$, with one electron having $+\frac{1}{2}$ and the other having $-\frac{1}{2}$.As a result, an orbital can hold a maximum of only two electrons.This rule is directly related to the quantum numbers of electrons.It is not concerned with the number of valence electrons, the order of filling orbitals by energy, or the filling of degenerate orbitals.Answer:D. quantum numbers of electrons