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Q.
Which of the following molecules/ions does not contain unpaired electrons?
Chemical Bonding and Molecular Structure
Solution:
The molecular orbital configuration of $\mathrm{O}_{2}^{2-}$ ion is $K K \sigma(2 s)^{2} \sigma^{*}(2 s)^{2} \sigma\left(2 p_{z}\right)^{2} \pi\left(2 p_{x}\right)^{2} \pi\left(2 p_{y}\right)^{2} \pi^{*}\left(2 p_{x}\right)^{2} \pi^{*}\left(2 p_{y}\right)^{2}$
Here, $K K$ represents non-bonding molecular orbital of $1 s$ orbital.
$\mathrm{O}_{2}^{2-}$ contains no unpaired electrons. The molecular orbital configuration of $\mathrm{B}_{2}$ molecule is $K K \sigma(2 s)^{2} \sigma^{*}(2 s)^{2} \pi\left(2 p_{x}\right)^{1} \pi\left(2 p_{y}\right)^{1}$
It contains 2 unpaired electrons.
The molecular orbital configuration of $\mathrm{N}_{2}^{+}$ ion is $K K \sigma(2 s)^{2} \sigma^{*}(2 s)^{2} \sigma\left(2 p_{z}\right)^{2} \pi\left(2 p_{x}\right)^{2} \pi\left(2 p_{y}\right)^{2} \sigma\left(2 p_{z}\right)^{1}$
It contains one unpaired electron.
The molecular orbital configuration of $\mathrm{O}_{2}$ molecule is $K K \sigma(2 s)^{2} \sigma^{\star}(2 s)^{2} \pi\left(2 p_{x}\right)^{2} \pi\left(2 p_{y}\right)^{2} \sigma\left(2 p_{z}\right)^{2} \pi^{*}\left(2 p_{x}\right)^{1} \pi^{*}\left(2 p_{y}\right)^{1}$
It contains 2 unpaired electrons.