Why `B_(2)` is paramagnetic in nature while `C_(2)` is not?

Explanation

The molecular orbital electronic configuration of both `B_(2) and C_(2)` are:
`B_(2):[sigma1s]^(2)[sigma^(**)1s]^(2)[sigma^(**)2s]^(2)[sigma^(**)2s]^(2)[pi2p_(x)]^(1)[pi2p_(y)]^(1)`
`B_(2):[sigma1s]^(2)[sigma^(**)1s]^(2)[sigma^(**)2s]^(2)[sigma^(**)2s]^(2)[pi2p_(x)]^(2)[pi2p_(y)]^(2)`
Since `B_(2)` has two unpaired electrons, therefore, `B_(2)` is paramagnetic.
`C_(2)` has no unpaired electron, therefore, `C_(2)` is diamagnetic.