Which of the following is diamagnetic ?

Options

A. `H_(2)^(+)`
B. `O_(2)`
C. `Li_(2)`
D. `He_(2)^(+)`

Answer

C

Explanation

Molecular orbital configuration of `H_(2)^(+) rArr sigma 1s^(1)` . It contains one unpaired electron, hence paramagnetic.
`O_(2)rArr sigma 1s^(2)sigma^(**)1s^(2)sigma2s^(2)sigma^(**)2s^(2)sigma 2p_(z)^(2)pi 2p_(x)^(2)pi 2 p_(y)^(2)pi^(**)2p_(x)^(1)pi^(**)2p_(y)^(1)`
It contains two unpaired electrons, hence paramagnetic.
`Li_(2)rArr sigma 1s^(2)sigma^(**)1s^(2)sigma 2s^(2)`. It does not contain any unpaired electron, hence diamagnetic.
`He_(2)^(+) rArr sigma 1s^(2)sigma^(**)1s^(1)`. It contains one unpaired electron, hence paramagnetic.