Which of the following is paramagentic?

Options

A. `O_(2)^(-)`
B. `CN`
C. `CO`
D. `NO^(+)`

Answer

A

Explanation

`CN^(-), CO and NO^(+)` are isolectronic with `14` electron each and there is no unpaired electrons in the `MO` configuration of these species. So these are diamagnetic , `O_(2)^(+)` is paramagnetic due to the presence of one unpaired electron.
`(CN^(-), CO, CO^(+))14 = sigma 1s^(2), sigma ** 1s^(2), sigma 2s^(2), sigma** 2s^(2), sigma 2p_(x)^(2)`
`pi 2p_(z)^(2) = pi 2p_(z)^(2)` (No unpaired electron diamagnetic)
`O_(2^(+)) = sigma 1s^(2), sigma ** 1s^(2), sigma 2s^(2), sigma** 2s^(2), sigma 2p_(x)^(2)`
` pi 2p_(x)^(2) = pi 2p_(z)^(2), pi ** 2p_(y)^(2) = pi ** 2p_(z)^(1)`
(One unpaired electron , paramagnetic)