Explanation

(d)
The molecular configuration of $O_{2}^{-}$ is as
$\sigma 1s^{2},\ _{\sigma}^{*}1s^{2}\ ,\sigma 2s^{2},\ _{\sigma}^{*}2s^{2},\sigma 2p_{z}^{2}\ ,\ \pi 2p_{y}^{2} \approx \pi 2p_{z}^{2},\ _{\pi}^{*}2p_{x}^{2} \approx \ _{\pi}^{*}2p_{y}^{2}$
Bond order = $\frac{N_{b - \ }N_{a\ }}{2}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = \frac{10 - 8}{2}$
$\therefore Bond\ order = 1$