Which one of the following has no unpaired electrons?

(a) In \(\mathrm{O}_{2}^{-}\)total number of electrons
\[
=16+1=17
\]
\(\therefore\) Orbital arrangement
\[
\begin{aligned}
=K K^{\prime}, \sigma 2 s^{2}, \sigma 2 s^{2}, \sigma 2 p_{z}^{2}, \pi 2 p_{x}^{2}=\pi 2 p_{y}^{2}, \\
\pi 2 p_{x}^{2} &=\pi 2 p_{y}^{1}
\end{aligned}
\]
(b) In \(\mathrm{O}_{2}^{+}\), total number of electrons
\[
=16-1=15
\]
\(\therefore\) Orbital arrangement \(=\mathrm{KK}^{\prime}, \sigma 2 \mathrm{~s}^{2}, \sigma 2 \mathrm{~s}^{2}\),
\[
\sigma 2 \mathrm{p}_{\mathrm{z}}^{2}, \pi 2 \mathrm{p}_{\mathrm{x}}^{2}=\pi 2 \mathrm{p}_{\mathrm{y}}^{2}, \stackrel{\approx}{\pi} 2 \mathrm{p}_{\mathrm{x}}^{1}
\]
(c) In \(\mathrm{O}_{2}^{2-}\), total number of electrons
\[
=16+2=18
\]
\(\therefore\) Orbital arrangement \(=K_{K}^{\prime}, \sigma 2 \mathrm{~s}^{2}, \sigma 2 \mathrm{~s}^{2}\), \(\sigma 2 \mathrm{p}_{\mathrm{z}}^{2}, \pi 2 \mathrm{p}_{\mathrm{x}}^{2}=\pi 2 \mathrm{p}_{\mathrm{y}}^{2} \pi 2 \mathrm{p}_{\mathrm{x}}^{2}=\pi 2 \mathrm{p}_{\mathrm{y}}^{2}\)
(d) In \(\mathrm{O}_{2}\), total number of electrons \(=16\)
\(\therefore\) Orbital arrangement \(=K K K^{\prime}, \sigma 2 s^{2}, \sigma^{*} 2 s^{2}\),
\(\sigma 2 \mathrm{p}_{\mathrm{z}}^{2}, \pi 2 \mathrm{p}_{\mathrm{x}}^{2} \approx \pi 2 \mathrm{p}_{\mathrm{y}}^{2}, \stackrel{\approx}{\pi} 2 \mathrm{p}_{\mathrm{x}}^{1} \approx \pi / 2 \mathrm{p}_{\mathrm{y}}^{1}\)
Hence, only \(\mathrm{O}_{2}^{2-}\) has no unpaired electrons.