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Select the correct set in which all species are paramagnetic.

1. NO, O2+, O2-, B2
2. B2, O2, N2, N2+
3. O2, O2+, O2-, N2+
4. Be2, He2, C2, N2

Correct answer: NO, O2+, O2-, B2

Solution

NO (15e):...pi*(2p)¹ => 1 unpaired => paramagnetic. O2+ (15e):...pi*(2p)¹ => paramagnetic. O2- (17e):...pi*(2p)³ => 1 unpaired => paramagnetic. B2 (10e):...pi(2p)¹ pi(2p)¹ (degenerate, one each by Hund) => 2 unpaired => paramagnetic. All four in option A are paramagnetic. N2 in option B is diamagnetic (0 unpaired). He2 and Be2 in option D do not exist as stable molecules and are diamagnetic.

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