The bond order and the magnetic characteristic of C N - are

According to MOT (If $\mathrm{z}$ is internuclear axis) The configuration of

${\text{CN}}^{-}:\mathrm{\sigma }1{\mathrm{s}}^2,\mathrm{\sigma }*1{\mathrm{s}}^2,\mathrm{\sigma }2{\mathrm{s}}^2,\mathrm{\sigma }*2{\mathrm{s}}^2,\mathrm{\pi }2{\mathrm{p}}_{\mathrm{x}}^2=\mathrm{\pi }2{\mathrm{p}}_{\mathrm{y}}^2,\mathrm{\sigma }2{\mathrm{p}}_{\mathrm{z}}^2$
 
Bond order$=$$\frac{\mathrm{number} \mathrm{of} \mathrm{electrons} \mathrm{in} \mathrm{bonding} \mathrm{orbitals}-\mathrm{number} \mathrm{of} \mathrm{electrons} \mathrm{in} \mathrm{anti}-\mathrm{bonding} \mathrm{orbitals}}{2}$

$\text{Bond order }=\frac{1}{2}(10-4)=3$

${\text{CN}}^{-}$ is diamagnetic due to absence of unpaired electron.