Which statement describes Hund's Rule?

Which statement describes Hund's Rule?

• A. Electrons fill the lowest-energy orbital first
• B. Electrons pair up in the same orbital before occupying others
• C. Single electrons with the same spin occupy each equal-energy orbital before any pairing occurs
• D. The Pauli exclusion principle requires opposite spins in the same orbital

Answer: (C)

Hund's Rule describes how electrons choose among orbitals of equal energy within a subshell. When those degenerate orbitals are available, electrons first occupy each orbital singly with the same spin before any pairing occurs. This arrangement lowers the overall energy of the atom due to exchange interactions and results in the maximum total spin for that subshell. For example, in a p^3 configuration, each of the three p orbitals gets one electron with the same spin, rather than pairing two electrons in one orbital while leaving others empty. The other statements describe related but different ideas: filling the lowest-energy orbital first is the Aufbau principle, pairing before all orbitals are singly occupied contradicts Hund’s rule, and the Pauli exclusion principle governs that two electrons in the same orbital must have opposite spins, not how electrons distribute among degenerate orbitals.

Hund's Rule describes how electrons choose among orbitals of equal energy within a subshell. When those degenerate orbitals are available, electrons first occupy each orbital singly with the same spin before any pairing occurs. This arrangement lowers the overall energy of the atom due to exchange interactions and results in the maximum total spin for that subshell. For example, in a p^3 configuration, each of the three p orbitals gets one electron with the same spin, rather than pairing two electrons in one orbital while leaving others empty. The other statements describe related but different ideas: filling the lowest-energy orbital first is the Aufbau principle, pairing before all orbitals are singly occupied contradicts Hund’s rule, and the Pauli exclusion principle governs that two electrons in the same orbital must have opposite spins, not how electrons distribute among degenerate orbitals.