Final answer:
The configuration that violates Hund's rule is B) 1s² 2s¹, as it suggests filling the 2s orbital before 2p orbitals are singly occupied.
Step-by-step explanation:
The electron configuration that violates Hund's rule is option B) 1s² 2s¹. Hund's rule states that electrons must fill degenerate orbitals separately before pairing up. Configuration B suggests an empty spot in the 2s orbital while there could still be unpaired electrons in the 2p orbitals, which violates this rule. Options A), C), and D) all adhere to Hund's rule, with electrons filling up their respective orbitals correctly: A) is completely filled, C) has three electrons in three separate 2p orbitals, and D) has a filled 2p sublevel.