The bond order of ${\mathrm{CN}}^{-}$ is

Valence electrons in ${\mathrm{CN}}^{-}=10$ Electronic configuration $\left(\sigma 2\mathrm{s}{)}^2\right(\sigma \ast 2\mathrm{s}{)}^2{\left(\pi 2{\mathrm{p}}_x\right)}^2{\left(\pi 2{\mathrm{p}}_y\right)}^2{\left(\sigma 2{\mathrm{p}}_z\right)}^2$

$\text{ Bond order }=\frac{(\text{ Bonding }-\text{ antibonding })\text{ electrons }}{2}=\frac{8-2}{2}=3$