Concept: The foundational rules of quantum mechanics govern how electrons populate atoms to prevent the physical impossibility of two identical fermions occupying the exact same space and state.
Formula: None required.
Solution: - The Pauli Exclusion Principle explicitly states that no two electrons in a single atom can have an identical set of all four quantum numbers (\(n, l, m, s\)).
- Even if two electrons share the same orbital (meaning \(n, l\), and \(m\) are identical), they must have opposite spins (one \(s = +1/2\), the other \(s = -1/2\)).
Why other options are incorrect: The Aufbau principle dictates the order of energy filling (lowest energy first). Hund's rule dictates that electrons singly occupy degenerate orbitals before pairing up.
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