This states that every orbital in a sublevel is singly occupied before any orbital is doubly occupied and that all electrons in singly occupied orbitals have the same spin.

This states that every orbital in a sublevel is singly occupied before any orbital is doubly occupied and that all electrons in singly occupied orbitals have the same spin.

• A. Aufbau principle
• B. Hund's rule
• C. Pauli's Exclusion Principle
• D. Heisenberg Principle

Answer: (B)

Hund’s rule is being tested here. In a given subshell, the available orbitals are degenerate, meaning they have the same energy. Electrons will first occupy each of these orbitals singly, with their spins aligned in the same direction, before any orbital gets a second electron. This setup maximizes the total spin and spreads electrons across different orbitals, which lowers the energy due to exchange interactions and reduces repulsion. Only after all orbitals in the subshell contain one electron do electrons begin to pair up in orbitals. The other principles describe different ideas: the Aufbau principle covers the order in which orbitals are filled by energy, the Pauli Exclusion Principle forbids two electrons from sharing the same set of quantum numbers, and the Heisenberg Principle deals with fundamental limits on simultaneously knowing certain pairs of properties.

Hund’s rule is being tested here. In a given subshell, the available orbitals are degenerate, meaning they have the same energy. Electrons will first occupy each of these orbitals singly, with their spins aligned in the same direction, before any orbital gets a second electron. This setup maximizes the total spin and spreads electrons across different orbitals, which lowers the energy due to exchange interactions and reduces repulsion. Only after all orbitals in the subshell contain one electron do electrons begin to pair up in orbitals. The other principles describe different ideas: the Aufbau principle covers the order in which orbitals are filled by energy, the Pauli Exclusion Principle forbids two electrons from sharing the same set of quantum numbers, and the Heisenberg Principle deals with fundamental limits on simultaneously knowing certain pairs of properties.