Question

Which of the following is paramagnetic?

• A. O₂
• B. CN^-
• C. CO
• D. NO⁺

Answer 1

Answer: (A)

A molecule having one or more unpaired electrons in their valence shell is paramagnetic or having an odd electron system is paramagnetic.
MO electronic configuration of ${\text{O}}_2$ is
$\sigma 1{\text{s}}^2\text{, }\sigma 1^{\star }{\text{s}}^2\text{, }\sigma 2{\text{s}}^2\text{, }\sigma 2^{\star }{\text{s}}^2$
$\sigma 2{\text{p}}_{\text{z}}^2\text{, }\pi 2{\text{p}}_{\text{x}}^2\text{, }\pi 2{\text{p}}_{\text{y}}^2\text{, }\pi 2^{\star }{\text{p}}_{\text{y}}^1\text{, }\pi 2^{\star }{\text{p}}_{\text{x}}^1$
Due to presence of unpaired electron in ABMO $\pi \stackrel{\star }{2}\text{px}$ & $\pi \stackrel{\star }{2}\text{py}$ behaves paramagnetic.