Which one of the following is not paramagnetic?

Solution :
Paramagnetic character is shown by those atoms or molecules which have unpaired electrons. In the given compounds $$CO$$  is not paramagnetic since, it does not have unpaired electrons. The configuration of $$CO$$  molecule is
$$CO\left( {14} \right) = \sigma 1{s^2},\mathop \sigma \limits^* 1{s^2},\sigma 2{s^2},$$      $$\mathop \sigma \limits^* 2{s^2},\sigma 2p_x^2,\pi 2p_y^2 \approx \pi 2p_z^2$$