Explanation:
\[\begin{array}{l}
\left( {\sigma {\rm{1}}{{\rm{s}}^{\rm{2}}}{\sigma ^{\rm{*}}}{\rm{1}}{{\rm{s}}^{\rm{2}}}\sigma {\rm{2}}{{\rm{s}}^{\rm{2}}}{\sigma ^{\rm{*}}}{\rm{2}}{{\rm{s}}^{\rm{2}}}\pi {\rm{2p}}_{\rm{x}}^{\rm{2}} \equiv \pi {\rm{2p}}_{\rm{y}}^{\rm{2}}\sigma {\rm{2p}}_{\rm{z}}^{\rm{2}}} \right)\\
{\rm{ Bond order }} = \frac{1}{2}\left( {\;{{\rm{N}}_b} - {{\rm{N}}_a}} \right)\\
\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \frac{1}{2}(10 - 4) = 3.0
\end{array}\]