- ✓$NO^-$
- B$NO^+$
- C$CN^-$
- D$N_2$
$NO ^{-}$contains $16$ electrons ( $7$ from nitrogen, $8$ from oxygen, add $1$ more for negative charge).
$NO ^{+}$has $14$ electrons ( $7$ from nitrogen, $8$ from oxygen, subtract $1$ for positive charge).
$CN ^{-1}$ has $14$ electrons ( $7$ from nitrogen, $6$ from carbon, add $1$ more for negative charge).
$N _2$ has $14$ electrons ( $7$ from nitrogen each).
The species containing the same number of electrons have the same bond order.
So $NO ^{-}$is the only one which has bond order different. So option $A$ is correct.
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(Given $R=2.0 \mathrm{cal} \mathrm{K}^{-1} \mathrm{~mol}^{-1}$ )

