Which of the following is paramagnetic ?

Options

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

Answer

A

Explanation

`CN^(-1), CO and NO^(+)` are isoelectronic species containing 14 electrons each. Their molecular electronic configuration can be represented as `sigma(1s)^2 sigma^**(1s)^2 sigma(2s)^2 sigma^**(2s)^2sigma(2p_z)^2 pi(2p_x)^2 pi(2p_y)^2`
As there is no unpaired electron so all these are diamagnetic in nature.
The M.O. configuration of` O_2` molecules is `sigma(1s)^2 sigma^**(1s)^2 sigma(2s)^2 sigma^**(2s)^2sigma(2p_z)^2 pi(2p_x)^2 pi(2p_y)^2 pi^**(2p_x)^1 pi^** (2p_y)^1`
Thus, there are two unpaired electrons in `O_2` so it is paramagnetic in nature.