Question

Assertion: $B_2$ molecule is diamagnetic.
Reason: The highest occupied molecular orbital is of $\sigma$ type.

• A. Assertion and Reason are true and the Reason is a correct explanation of the Assertion
• B. Assertion and Reason are true but Reason is not a correct explanation of the Assertion
• C. Assertion is true but Reason is false
• D. Both the Assertion and Reason are false
• E. Assertion is false but the Reason is true

Answer 1

The correct option is D Both the Assertion and Reason are false

$B_2$ molecule has no. of electrons $=10$
Molecular orbital configuration:
$\sigma {\left(1s\right)}^2{\sigma }^{\ast }{\left(1s\right)}^2\sigma {\left(2s\right)}^2{\sigma }^{\ast }{\left(2s\right)}^2\pi 2p_x^1\pi 2p_y^1$
Due to unpaired electron, it is paramagnetic.
The highest occupied $MO$ is of $\pi$- type.

Hence, both the assertion and reason are false.