Question

which 2p subshell has the electrons properly placed?
○ 2p ↑↑ ↑↑ ↑
○ 2p ↑↓ ↑ ↓
○ 2p ↑↑ ↑↑
○ 2p ↑↓ ↑↓ ↑
○ 2p ↑↑ ↑ ↑

Explanation:

According to Hund's rule, electrons in degenerate orbitals (same - energy orbitals in a sub - shell) first fill each orbital singly with parallel spins before pairing up. The 2p sub - shell has 3 degenerate orbitals. The correct electron filling pattern has electrons filling each of the 3 orbitals singly with parallel spins first.

Answer:

The option with three single - occupied 2p orbitals and electrons having parallel spins (the last option among the ones shown in the typical visual representation where arrows are all pointing in the same direction in the three 2p boxes) is the correct one for proper electron placement in the 2p sub - shell according to Hund's rule.