b
\(\left(12 \mathrm{e}^{-}\right): \sigma 1 \mathrm{~s}^2, \sigma^* 1 \mathrm{~s}^2, \sigma 2 \mathrm{~s}^2, \sigma^* 2 \mathrm{~s}^2\left[\pi 2 \mathrm{p}_{\mathrm{x}}^2=\pi 2 \mathrm{p}_{\mathrm{y}}^2\right]\)

\(\text { B.O. }=\frac{8-4}{2}=2\)

\(\mathrm{O}_2\)

\(\left(16 \mathrm{e}^{-}\right): \sigma 1 \mathrm{~s}^2, \sigma^* 1 \mathrm{~s}^2, \sigma 2 \mathrm{~s}^2, \sigma^* 2 \mathrm{~s}^2, \sigma 2 \mathrm{pz}^2\)

\({\left[\pi 2 \mathrm{p}_{\mathrm{x}}^2=\pi 2 \mathrm{p}_{\mathrm{y}}^2\right]\left[\pi^* 2 \mathrm{p}_{\mathrm{x}}^1=\pi^* 2 \mathrm{p}_{\mathrm{y}}^1\right]}\)

\(\text { B.O. }=\frac{10-6}{2}=2\)

\(\mathrm{Be}_2\)

\(\left(8 \mathrm{e}^{-}\right): \sigma 1 \mathrm{~s}^2, \sigma^* 1 \mathrm{~s}^2, \sigma 2 \mathrm{~s}^2, \sigma^* 2 \mathrm{~s}^2\)

\(\text { B.O. }=\frac{4-4}{2}=0\)

\(\text { Li }_2\)

\(\left(6 \mathrm{e}^{-}\right): \sigma 1 \mathrm{~s}^2, \sigma^* 1 \mathrm{~s}^2, \sigma 2 \mathrm{~s}^2\)