Explanation

(c)
$O_{2}(16) = \sigma 1s^{2},\ \ _{\sigma}^{*}1s^{2},\ \sigma 2s^{2},\ _{\sigma}^{*}2s^{2},\ \sigma 2p_{z}^{2},\ \pi 2p_{x}^{2} \approx \ \pi 2p_{y}^{2},\ _{\pi}^{*}2p_{x}^{1}\ \approx \ _{\pi}^{*}2p_{y}^{1}$
BO $= \frac{10 - 6}{2} = 2$
$O_{2}^{2 -}(18) = \sigma 1s^{2},\ \ _{\sigma}^{*}1s^{2},\ \sigma 2s^{2},\ _{\sigma}^{*}2s^{2},\ \sigma 2p_{z}^{2},\ \pi 2p_{x}^{2} \approx \ \pi 2p_{y}^{2},\ _{\pi}^{*}2p_{x}^{2}\ \approx \ _{\pi}^{*}2p_{y}^{2}$
BO $= \frac{10 - 8}{2} = 1$
$N_{2}(14) = \sigma 1s^{2},\ \ _{\sigma}^{*}1s^{2},\ \sigma 2s^{2},\ _{\sigma}^{*}2s^{2},\ \pi 2p_{x}^{2} \approx \pi 2p_{y}^{2},\sigma 2p_{z}^{2}$
BO $= \frac{10 - 4}{2} = 3$
Thus, bond order is highest for $N_{2}$.