To determine the bond order and magnetic nature of B\u2082, we first write its molecular orbital (MO) configuration. Boron (B) has an atomic number of 5, so its electronic configuration is 1s\u00b2 2s\u00b2 2p\u00b9. A B\u2082 molecule has a total of 10 electrons (5 from each B atom).

The order of filling molecular orbitals for molecules with up to 14 electrons (like B\u2082) is:

\u03c31s, \u03c3*1s, \u03c32s, \u03c3*2s, \u03c02p\u2093 = \u03c02p\u2098, \u03c32p\u2090, \u03c0*2p\u2093 = \u03c0*2p\u2098, \u03c3*2p\u2090

Step 1: Fill the molecular orbitals with 10 electrons.

MO configuration of B\u2082: (\u03c31s)\u00b2 (\u03c3*1s)\u00b2 (\u03c32s)\u00b2 (\u03c3*2s)\u00b2 (\u03c02p\u2093)\u00b2

Note: Normally, for B\u2082, the \u03c02p orbitals are degenerate and filled according to Hund's rule, meaning one electron in each \u03c02p\u2093 and \u03c02p\u2098 orbital, leading to paramagnetism. However, the question states that Hund's rule is violated. This means that instead of filling the degenerate \u03c02p\u2093 and \u03c02p\u2098 orbitals with one electron each, both electrons will pair up in one of the \u03c02p orbitals (e.g., \u03c02p\u2093).

Step 2: Calculate the bond order.

Bond Order (BO) = $\frac{1}{2}$ (Number of electrons in bonding MOs - Number of electrons in antibonding MOs)

Bonding electrons (N\u209b) = 2 (in \u03c31s) + 2 (in \u03c32s) + 2 (in \u03c02p\u2093) = 6

Antibonding electrons (N\u2092) = 2 (in \u03c3*1s) + 2 (in \u03c3*2s) = 4

BO = $\frac{1}{2}$ (6 - 4) = $\frac{1}{2}$ (2) = 1

Step 3: Determine the magnetic nature.

Since all electrons in the MO configuration are paired (due to the violation of Hund's rule, the two electrons in the \u03c02p orbital are paired), the molecule is diamagnetic.

Option Analysis:

• A) 1 and diamagnetic: This matches our calculated bond order and magnetic nature when Hund's rule is violated.
• B) 0 and paramagnetic: Incorrect bond order and magnetic nature.
• C) 0 and diamagnetic: Incorrect bond order.
• D) 1 and paramagnetic: Incorrect magnetic nature. If Hund's rule were followed, B\u2082 would be paramagnetic with a bond order of 1.

Correct Answer: (A)