Question

Assertion : $O_{2}$ molecule is diamagnetic while $C_{2}$ molecule is paramagnetic in nature.
Reason: Bond order of $O_ 2$ molecule is $1.5$ and that of $C_2$ molecule is $2.5$.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (D)

$O_{2}: \left(\sigma 1s\right)^{2} \left(\sigma^* 1s\right)^{2}\left(\sigma 2s\right)^{2}\left(\sigma^* 2s\right)^{2} \left(\sigma 2p_{z}\right)^{2}$
$ \left(\pi 2p_{x}^{2} = \pi 2p_{y}^{2}\right) \left(\pi^* 2p_{x}^{1} =\pi^* 2p_{y}^{1} \right)$
Bond order $= \frac{1}{2} \left(N_{b} -N_{a}\right) $
$= \frac{1}{2}\left(10-6\right) = 2$
It contains two unpaired electrons hence it is paramagnetic in nature.
$ C_{2} : \left(\sigma 1s\right)^{2} \left(\sigma^* 1s\right)^{2}\left(\sigma 2s\right)^{2}\left(\sigma^* 2s\right)^{2} \left(\pi 2p_{x}^{2} = \pi 2p_{y}^{2}\right)$
Bond order $= \frac{1}{2} (8-4) = 2$
All electrons are paired hence it is diamagnetic in nature.