$\begin{aligned}
& \mathrm{O}2(16 \mathrm{e}):\left(\sigma{1 \mathrm{s}}\right)^2\left(\sigma_{1 \mathrm{s}}^\right)^2\left(\sigma_{2 \mathrm{s}}\right)^2\left(\sigma_{2 \mathrm{s}}^\right)^2 \
& \left(\sigma_{2 \mathrm{p}}\right)^2\left[\left(\pi_{2 \mathrm{p}}\right)^2=\left(\pi_{2 \mathrm{p}}\right)^2\right],\left[\left(\pi_{2 \mathrm{p}}^\right)^1=\left(\mathrm{m}_{2 \mathrm{p}}^\right)^1\right]
\end{aligned}$
Number of e−present in (π∗) of O2=2 Number of e−present in (π∗) of O2+=1 Number of e−present in (π∗) of O2−=3 So total e−in (π∗)=2+1+3=6