Which one of the following is expected to have maximum bond length?

Solution:

Electronic configuration follows the order $\left(\sigma 2\mathrm{s}\right)(\sigma \ast 2\mathrm{s})\left(\pi 2{\mathrm{p}}_x\right)\left(\pi 2{\mathrm{p}}_y\right)\left(\sigma 2{\mathrm{p}}_z\right)\left({\pi }^{\ast }2{\mathrm{p}}_x\right)$

${\mathrm{NO}}^{+}$(valence electrons =10);  Bond order $=(8-2)/2=3$

${\mathrm{NO}}^{2+}$(valence electrons = 9);  Bond order $=(7-2)/2=2.5$

$\mathrm{NO}$ (valence electrons =11);  Bond order $=(8-3)/2=2.5$

${\mathrm{NO}}^{-}$(valence electrons =12);  Bond order $=(8-4)/2=2.0$

Smaller the bond order, larger the bond length. Hence,  ${\mathrm{NO}}^{-}$ will having maximum bond length.