Explain why Cu(I) is diamagnetic while Cu(II) is paramagnetic in nature?

Explanation

Electronic configuration of `Cu (Z=29), Cu^(+), Cu^(2+)` as follows:
`Cu (Z = 29): [Ar]^18 3d^10 4s^1`


Cu (I) is diamagnetic because it has 3do configuration and therefore is not unpaired electron on the other hand Cu(II) has 3do configuration and there is unpaired electron. So Cu (II) is Paramagnetic in nature.