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Q.
During change of $O_2$ to $O_2^-$ ion, the electron adds on
which one of the following orbitals?
Chemical Bonding and Molecular Structure
Solution:
Electronic configuration of $\mathrm{O}_{2}$
$\sigma(1 s)^{2} \sigma^{*}(1 s)^{2} \sigma(2 s)^{2} \sigma^{*}(2 s)^{2} \sigma\left(2 p_{z}\right)^{2} \pi\left(2 p_{x}\right)^{2} \pi\left(2 p_{y}\right)^{2}$
$\pi^{*}\left(2 p_{x}\right)^{1} \pi^{*}\left(2 p_{y}\right)^{1}$
Thus, the incoming electron will enter in $\pi^{*} 2 p_{x}$ to form $\mathrm{O}_{2}^{-}$