alleryHund's rule applies during the filling of
Asubshells of decreasing energy
Bdifferent shells in order of increasing $n$
Coutermost shell only
Da single subshell with degenerate orbitals (singly first, then pair)
Answer & Solution
Correct answer: D. a single subshell with degenerate orbitals (singly first, then pair)
Within a degenerate set (e.g., the three 2p orbitals), electrons occupy orbitals singly with parallel spins before pairing — minimises electron–electron repulsion.
The half-filled-stability of N ($2p^3$) is a Hund's rule consequence.
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