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JEE Main 2023 · Chemistry · Chemical Bonding and Molecular Structure · medium

Which pair contains species that both have bond order 2.5 and are paramagnetic?

Single correct option

Which pair contains species that both have bond order 2.52.5 and are paramagnetic?
  1. A. O2+\mathrm{O_2^+} and N2+\mathrm{N_2^+}
  2. B. N2+\mathrm{N_2^+} and CN−\mathrm{CN^-}
  3. C. O2−\mathrm{O_2^-} and NO\mathrm{NO}
  4. D. C2\mathrm{C_2} and B2\mathrm{B_2}
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Answer: (A) O2+\mathrm{O_2^+} and N2+\mathrm{N_2^+}

By MO theory: O2+\mathrm{O_2^+} (15 valence-type electrons; π∗\pi^* has 1 electron): BO=(10−5)/2=2.5BO=(10-5)/2=2.5, one unpaired electron. N2+\mathrm{N_2^+} (13 electrons): BO=(9−4)/2=2.5BO=(9-4)/2=2.5, one unpaired electron in σ2p\sigma_{2p}. CN−\mathrm{CN^-} is isoelectronic with N2\mathrm{N_2} (BO=3BO=3, diamagnetic). O2−\mathrm{O_2^-} has BO=1.5BO=1.5. C2\mathrm{C_2} has BO=2BO=2 and is diamagnetic. B2\mathrm{B_2} has BO=1BO=1. Only option (A) satisfies both conditions.
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