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)

$O_2:{\left(\sigma 1s\right)}^2{\left({\sigma }^{\ast }1s\right)}^2{\left(\sigma 2s\right)}^2{\left({\sigma }^{\ast }2s\right)}^2{\left(\sigma 2p_z\right)}^2$
$\left(\pi 2p_x^2=\pi 2p_y^2\right)\left({\pi }^{\ast }2p_x^1={\pi }^{\ast }2p_y^1\right)$
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.
$C_2:{\left(\sigma 1s\right)}^2{\left({\sigma }^{\ast }1s\right)}^2{\left(\sigma 2s\right)}^2{\left({\sigma }^{\ast }2s\right)}^2\left(\pi 2p_x^2=\pi 2p_y^2\right)$
Bond order $=\frac{1}{2}(8-4)=2$
All electrons are paired hence it is diamagnetic in nature.