Assuming `2s-2p` mixing is `NOT` operative, the paramagnetic species among the following is .

Options

A. `Be_(2)`
B. `B_(2) `
C. `C_(2) `
D. `N_(2)`

Answer

C

Explanation

This problem can be solved by using the concept involved in molecular orbital theory. Write the molecular orbital electronic configuration keeping in mind that there is no 2s-2p mixing, then if highest occupied molecular orbital contain unpaired electron then molecule is paramagnetic otherwise diamagnetic.
Assuming that no 2s-2p mixing takes place the molecular orbital electronic configuration can be written in the following sequence of
`sigma1s, overset(***)sigma1s, sigma2s overset(***)sigma2s, sigma2p_(z), pi 2p_(x)-=pi 2p_(y), overset(***)pi 2p_(x)-=overset(***)pi 2p_(y), overset(***)sigma 2p_(z)`
(a) `Be_(2) to sigma1s^(2), overset(***)sigma1s^(2), sigma2s^(2) overset(***)sigma2s^(2) ` (diamagnetic)
(b) `B_(2) to sigma1s^(2), overset(***)sigma1s^(2), sigma2s^(2), overset(***)sigma2s^(2), overset(***)sigma2p_(z)^(2), ""_(pi2p_(y)^(0))^(pi2p_(x)^(0))" "` (diamagnetic)
(c) `C_(2) to sigma1s^(2), overset(***)sigma1s^(2), sigma2s^(2), overset(***)sigma2s^(2), overset(***)sigma2p_(z)^(2), ""_(pi2p_(y)^(1))^(pi2p_(x)^(1)), overset(***)pi 2p_(x)^(0), overset(***)sigma2p_(z)^(0)" "` (diamagnetic)
(d) `N_(2) to sigma1s^(2), overset(***)sigma1s^(2), sigma2s^(2), overset(***)sigma2s^(2), overset(***)sigma2p_(z)^(2), ""_(pi2p_(y)^(2))^(pi2p_(x)^(2)),""_(overset(***)pi 2p_(y)^(2))^(overset(***)pi2p_(x)^(0)), sigma***2p_(z)^(0) " "` (diamagnetic)
Hence, (C) is the correct choice.