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For homonuclear diatomic molecules of B₂, C₂, N₂, the correct MO energy ordering is:

A(π2p_x = π2p_y) < σ2s < σ*2s < σ2p_z < (π*2p_x = π*2p_y) < σ*2p_z
Bσ2s < (π2p_x = π2p_y) < σ*2s < σ2p_z < (π*2p_x = π*2p_y) < σ*2p_z
Cσ2s < σ*2s < σ2p_z < (π2p_x = π2p_y) < (π*2p_x = π*2p_y) < σ*2p_z
Dσ2s < σ*2s < (π2p_x = π2p_y) < σ2p_z < (π*2p_x = π*2p_y) < σ*2p_z
Answer & Solution
Correct answer: D. σ2s < σ*2s < (π2p_x = π2p_y) < σ2p_z < (π*2p_x = π*2p_y) < σ*2p_z
For B₂, C₂, N₂ (smaller atoms with significant s-p mixing), **π2p MOs lie *below* σ2p_z**. For O₂, F₂ (larger atoms, less mixing) the order flips so σ2p_z is below the π2p set.
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