Which of the following is paramagnetic?

Options

A. `CO`
B. `O_2^-`
C. `CN^-`
D. `NO^+`

Answer

B

Explanation

Paramagnetic species contains unpaired electrons in their molecular orbital electronic configuration.
Molecular orbital configuration of the given species is as
CO (6+8=14)
`=sigma1s^2 , overset***1s^2 , sigma2s^2 , overset***2s^2 , pi2p_x^2~~pi2p_y^2, sigma2p_z^2`
(All the electrons are paired so, it is diamagnetic )
`O_2^(-)`(8+8+1=17)
`=sigma1s^2 , overset***1s^2 , sigma2s^2 , overset***2s^2 ,sigma2p_z^2, pi2p_x^2~~pi2p_y^2, overset***pi2p_x^2~~overset***2p_y^1`
(It contains one unpaired electron so , it is paramagnetic )
`CN^-` (6+7+1=14) = same as CO
`NO^+` (7+8-1=14)=same as CO
Thus, among the given species only `O_2^-` is paramagnetic.