Which of the following species is not paramagnetic?

Options

A. NO
B. CO
C. `O_(2)`
D. `B_(2)`

Answer

B

Explanation

`NO to `one unparied electron is present in `pi^(**)` molecular orbit hence paramagnetic
`CO+ KK sigma (2s)^(2)(pi2p_(x))^(2)`
`=(pi 2p_(y))^(2)(sigma 2p_(z))^(2) sigma^(**) (2s)^(2)` no unparied electron hence diamagnetic.
(c) `O_(2) sigma (1s)^(2) sigma^(**) (1s)^(2) sigma (2s)^(2) sigma^(**) (2s)^(2) sigma (2p_(z))^(2)`
`pi(2p_(x))^(2)=pi(2p_(y))^(2) pi^(**) (2p_(x))^(1)=pi(2p_(y))^(1)`
two unparied electron hence paramagnetic.
`B_(2) to KK sigma (2s)^(2) sigma^(**) (2s)^(2) pi (2p_(x))^(1) =pi(2p_(y))^(1)`
`B_(2)` contains two unpaired electrons hence paramagnetic.