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JEE Main 2022 · Chemistry · Chemical Bonding and Molecular Structure · medium

Among N2^+, N2^-, O2^+, NO, O2^- and CN^-, the number of species that are paramagnetic and have bond order 2.5 is

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Among N2+\mathrm{N_2^+}, N2−\mathrm{N_2^-}, O2+\mathrm{O_2^+}, NO\mathrm{NO}, O2−\mathrm{O_2^-} and CN−\mathrm{CN^-}, the number of species that are paramagnetic and have bond order 2.52.5 is
  1. A. 4
  2. B. 2
  3. C. 3
  4. D. 5
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Answer: (A) 4

Count electrons in MOs. N2+\mathrm{N_2^+} (13 e−^-): bond order (9−4)/2=2.5(9-4)/2=2.5, one unpaired electron. N2−\mathrm{N_2^-} (15 e−^-): (10−5)/2=2.5(10-5)/2=2.5, one unpaired electron in π∗\pi^*. O2+\mathrm{O_2^+} (15 e−^-): (10−5)/2=2.5(10-5)/2=2.5, paramagnetic. NO\mathrm{NO} (15 e−^-): 2.52.5, one unpaired electron. O2−\mathrm{O_2^-} has bond order 1.51.5; CN−\mathrm{CN^-} has bond order 33 and is diamagnetic. Hence 4 species.
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