Question

Which of the following species are paramagnetic?

• A. $C{N}^{-}$
• B. $NO$
• C. $O_2^{-2}$
• D. $O_2$

Answer 1

Answer: (B), (D)

The correct options are
B $O_2$
D $NO$

1. $C{N}^{-}$:

valence electrons=$4+5+1=10$

${\left(\sigma 2s\right)}^2{(\sigma \ast 2s)}^2{\left(\sigma 2p\right)}^2{\left(\pi 2p\right)}^4$

2. $NO$:

valence electrons=$5+6=11$

${\left(\sigma 2s\right)}^2{(\sigma \ast 2s)}^2{\left(\sigma 2p\right)}^2{\left(\pi 2p\right)}^4{\left({\pi }^{\ast }2p\right)}^1$

3.$O_2^{2-}$

valence electrons=$6+6+2=14$

${\left(\sigma 2s\right)}^2{(\sigma \ast 2s)}^2{\left(\sigma 2p\right)}^2{\left(\pi 2p\right)}^4{\left({\pi }^{\ast }2p\right)}^4$

4.$O_2$:

valence electrons=$6+6=12$

${\left(\sigma 2s\right)}^2{(\sigma \ast 2s)}^2{\left(\sigma 2p\right)}^2{\left(\pi 2p\right)}^4{\left({\pi }^{\ast }2p_x\right)}^1{\left({\pi }^{\ast }2p_y\right)}^1$

Therefore $NO$ and $O_2$ have unpaired electrons, and will thus be paramagnetic.

Hence, option $B$ and $D$ are correct.