Question

The paramagnetic behaviour of $B_2$ is due to the presence of:

• A. Two unpaired electrons in ${\pi }_{b}MO$
• B. Two unpaired electrons in $\stackrel{\ast }{\pi }MO$
• C. Two unpaired electron in $\stackrel{\ast }{\sigma }MO$
• D. Two unpaired electrons in ${\sigma }_{b}MO$

Answer 1

The correct option is A Two unpaired electrons in ${\pi }_{b}MO$

$B_2$ contains $5+5=10e^{-}$

$=\sigma 1s^2\stackrel{\ast }{\sigma }1s^2\sigma 2s^2\stackrel{\ast }{\sigma }2s^2\pi 2p_x^1\simeq \pi 2p_y^1$

Due to the presence of $2$ unpaired electrons, in $\pi$ bonding orbitals, $B_2$ shows paramagnetic behaviour.