JEE Main 2017 · Chemistry · Chemical Bonding and Molecular Structure · medium

Pairs of species have the same bond order but different numbers of unpaired electrons (ground state, molecular orbital theory)?

Single correct option

Which of the following pairs of species have the same bond order but different numbers of unpaired electrons (ground state, molecular orbital theory)?

A. $\mathrm{N_2^+}$ and $\mathrm{O_2^+}$
B. $\mathrm{N_2}$ and $\mathrm{CO}$
C. $\mathrm{NO}$ and $\mathrm{O_2^+}$
D. $\mathrm{C_2}$ and $\mathrm{O_2}$

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Answer: (D) $\mathrm{C_2}$ and $\mathrm{O_2}$

\mathrm{C_2}

(12 e

^-

\pi_{2p}^4

filled,

\sigma_{2p}

empty): bond order

2

, no unpaired electrons.

\mathrm{O_2}

: bond order

2

, two unpaired electrons in

\pi^*

. So they differ in unpaired electrons.

\mathrm{N_2^+}

\mathrm{O_2^+}

and

\mathrm{NO}

all have bond order

2.5

and one unpaired electron;

\mathrm{N_2}

and

\mathrm{CO}

both have bond order

3

and none.

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