Which of the following is paramagnetic?

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