Question

Assuming that Hund's rule is violated, the bond order and magnetic nature of the diatomic molecule $B_2$ is

• A. 1 and diamagnetic
• B. 0 and diamagnetic
• C. 1 and paramagnetic
• D. 0 and paramagnetic

Answer 1

Answer: (A)

For molecules lighter than $O_2$, the increasing order of energies of molecular orbitals is

where, $\pi 2p_y$ and $\pi 2p_z$ are degenerate molecular orbitals, first singly occupied and then pairing starts if Hund's rule is obeyed. If Hund's rule is violated in $B_2$, electronic arrangement would be

No unpaired electron-diamagnetic.
Bond order $=\frac{\text{ bonding electrons }-\text{ antibonding electrons }}{2}$
$=\frac{6-4}{2}=1$