Question

which electron configuration violates hunds rule?
answer:
a $\text{he}2s^2 2p_x^2 2p_y^2 2p_z^1$
b $\text{he}2s^2 2p_x^2 2p_y^1 2p_z^2$
c $\text{he}2s^2 2p_x^1 2p_y^2 2p_z^2$
d $\text{he}2s^2 2p_x^2 2p_y^2$
e $\text{he}2s^2 2p_x^1 2p_y^1 2p_z^2$
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Explanation:

Hund's rule states that electrons will occupy degenerate orbitals (like 2pₓ, 2pᵧ, 2p_z) singly with parallel spins before pairing up. We check each option:

• Options A, B, C, E have 5 total 2p electrons, which fill each orbital singly first then pair, following Hund's rule.
• Option D has 4 2p electrons but leaves the 2p_z orbital empty while pairing 2pₓ and 2pᵧ, violating Hund's rule (electrons should first occupy each 2p orbital singly before pairing).

Answer:

D. $[\text{He}]2\text{s}^22\text{p}_x^22\text{p}_y^2$