Which of the following orbital-filling diagrams for the 2p subshell violates Hund's rule?

• A. ↑ _ _
• B. ↑↓ ↑ _
• C. ↑ ↑↓ _
• D. ↑ ↑ ↑

Answer: (B)

Verified step by step guidance

1. Recall Hund's rule: electrons fill degenerate orbitals (orbitals with the same energy) singly first, with parallel spins, before pairing up in any one orbital.
2. Identify the 2p subshell orbitals: there are three 2p orbitals, each can hold up to two electrons with opposite spins.
3. Examine each orbital-filling diagram to see if electrons are placed singly in each orbital before any pairing occurs.
4. Check if any diagram shows paired electrons in one orbital while another orbital remains empty or singly occupied, which would violate Hund's rule.
5. Conclude that the diagram with paired electrons in one orbital and an empty orbital (like the one showing ↑↓ ↑ _) violates Hund's rule because electrons should occupy each orbital singly first.