Consider the following species : ${\mathrm{CN}}^{+},{\mathrm{CN}}^{-},\mathrm{NO} \mathrm{and} \mathrm{CN} .$Which one of these will have the highest bond order?

$\mathrm{NO}:(\mathrm{\sigma }1\mathrm{s}{)}^2,{\left({\mathrm{\sigma }}^{\star }1\mathrm{s}\right)}^2,(\mathrm{\sigma }2\mathrm{s}{)}^2,{\left({\mathrm{\sigma }}^{*}2\mathrm{s}\right)}^2,{\left(\mathrm{\sigma }2{\mathrm{p}}_{\mathrm{z}}\right)}^2,{\left(\mathrm{\pi }2{\mathrm{p}}_{\mathrm{x}}\right)}^2={\left(\mathrm{\pi }2{\mathrm{p}}_{\mathrm{y}}\right)}^2,{\left({\mathrm{\pi }}^{\star }2{\mathrm{p}}_{\mathrm{x}}\right)}^1={\left({\mathrm{\pi }}^{\star }2{\mathrm{p}}_{\mathrm{y}}\right)}^0$

$\text{ B. }\mathrm{O}.=\frac{10-5}{2}=2.5$

${\mathrm{CN}}^{-}:(\mathrm{\sigma }1\mathrm{s}{)}^2,{\left({\mathrm{\sigma }}^{\star }1\mathrm{s}\right)}^2,(\mathrm{\sigma }2\mathrm{s}{)}^2,{\left({\mathrm{\sigma }}^{*}2\mathrm{s}\right)}^2,{\left(\mathrm{\pi }2{\mathrm{p}}_{\mathrm{x}}\right)}^2={\left(\mathrm{\pi }2{\mathrm{p}}_{\mathrm{y}}\right)}^2,{\left(\mathrm{\sigma }2{\mathrm{p}}_{\mathrm{z}}\right)}^2$

$\text{ B.O. }=\frac{10-4}{2}=3$

$\mathrm{CN}:(\sigma 1s{)}^2,{\left({\sigma }^{\star }1s\right)}^2,(\sigma 2s{)}^2,{\left({\sigma }^{\star }2s\right)}^2,{\left(\pi 2p_x\right)}^2={\left(\pi 2p_y\right)}^2,{\left(\sigma 2p_z\right)}^1$

$\mathrm{B}.\mathrm{O}·=\frac{9-4}{2}=2.5$

${\mathrm{CN}}^{+}:(\mathrm{\sigma }1\mathrm{s}{)}^2,{\left({\mathrm{\sigma }}^{\star }1\mathrm{s}\right)}^2,(\mathrm{\sigma }2\mathrm{s}{)}^2,{\left({\mathrm{\sigma }}^{\star }2\mathrm{s}\right)}^2,{\left(\mathrm{\pi }2{\mathrm{p}}_{\mathrm{x}}\right)}^2={\left(\mathrm{\pi }2{\mathrm{p}}_{\mathrm{y}}\right)}^2$

$\text{ B.O. }=\frac{8-4}{2}=2$

$\mathrm{Hence}, {\mathrm{CN}}^{-}\mathrm{has} \mathrm{highest} \mathrm{bond} \mathrm{order}.$