Which one of the following pairs of species have the same bond order?

$\mathrm{Bond} \mathrm{order}=\frac{(\mathrm{Bonding}-\mathrm{antibonding})}{2}$

$$\begin{gathered} {\mathrm{O}}_2^{-}=\frac{10-7}{2}=1.5 \\ {\mathrm{CN}}^{-}=\frac{8-2}{2}=3 \\ \mathrm{CO}=\frac{10-4}{2}=3 \\ \mathrm{NO}=\frac{8-3}{2}=2.5 \end{gathered}$$ 

${\mathrm{CN}}^{-},\mathrm{CO}$ are iso-electronic species have same bond order.