Chemistry - CHEMICAL BONDING Question with Solution | TestHub

Paramagnetic species contains unpaired electrons in their molecular orbital electronic configuration. Molecular orbital configuration of the given species is as $$\begin{array}{rl}& \mathrm{CO}(6+8=14)=\sigma 1s^2,\stackrel{\ast }{\sigma }1s^2,\\ & \sigma 2s^2,\stackrel{\ast }{\sigma }2s^2,\pi 2p_x^2\approx \pi 2p_y^2,\sigma 2p_z^2\end{array}$$ (All the electrons are paired so it is diamagneitc.) $$\begin{array}{rl}& {\mathrm{O}}_2^{-}(8+8+1=17)\\ & =\sigma 1s^2,\stackrel{\ast }{\sigma }1s^2,\sigma 2s^2,\stackrel{\ast }{\sigma }2s^2,\sigma 2p_z^2,\pi 2p_x^2\\ & \approx \pi 2p_y^2,\stackrel{\ast }{\pi }2p_x^2\approx \stackrel{\ast }{\pi }2p_y^1\end{array}$$ It contains one unpaired electron so it is paramagnetic. $$\begin{array}{rl}& {\mathrm{CN}}^{-}(6+7+1=14)=\text{ same as }\mathrm{CO}\\ & {\mathrm{NO}}^{+}(7+8-1)=\text{ same as }\mathrm{CO}\end{array}$$ Thus, among the given species only ${\mathrm{O}}_2^{-}$is paramagnetic.