# Among the following species  , the diamagnetic molecule is : Option 1) $NO$ Option 2) $CO$ Option 3) $B_{2}$ Option 4) $O_{2}$

Energy level diagram for molecular orbitals. -

1S atomic orbitals combine to give   $\sigma (1S)$ and  $\sigma^{\ast}(1S).$ 2S and 2P atomic orbitals give rise to eight molecular orbitals.

- wherein

Magnetic behaviour of molecule -

If  all the molecular orbitals in a molecule are doubly occupied, the substance is diamagnetic

- wherein

However if one or more molecular orbital are singly occupied it is paramagnetic e.g. O2

If the molecular orbitals have unpaired electrons then the molecule will paramagnetic.

or if all are paired then the molecule will diamagnetic.

In CO, moleculer orbital configuration

$\sigma \:\:1S^{2},\sigma ^{*}\:\:1S^{2},\sigma \:\:2S^{2},\sigma ^{*}\:\:2S^{2},\pi_{2px}^{2}=\pi _{2py}^{2},\sigma 2p_{z}^{2}$

There are no unpaired electrons.

Option 1)

$NO$

Option 2)

$CO$

Option 3)

$B_{2}$

Option 4)

$O_{2}$

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