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Among the species H2, He2+, Li2, Be2, B2, C2, N2, O2-, and F2, how many are diamagnetic? (Atomic numbers: H = 1, He = 2, Li = 3, Be = 4, B = 5, C = 6, N = 7, O = 8, F = 9)

1. 4
2. 5
3. 6
4. 7

Correct answer: 5

Solution

Filling molecular orbitals: H2, Li2, C2, N2, and F2 have all electrons paired (diamagnetic), while He2+ (1 unpaired), B2 (2 unpaired), O2- (1 unpaired) are paramagnetic; Be2 (bond order 0) does not exist as a stable molecule. This gives 5 diamagnetic species.

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