Explanation

(c)
Molecular orbital configuration of $N_{2}^{+}$ is
$N_{2}^{+} = (\sigma 1s)^{2}\left( \ _{\sigma}^{*}1s \right)^{2}(\sigma 2s)^{2}\left( \ _{\sigma}^{*}2s \right)^{2}\left( \pi 2p_{y} \right)^{2} = \left( \pi 2p_{z} \right)^{2}\left( \sigma 2p_{x} \right)^{1}$
Bond order $= \frac{N_{b - \ }N_{a\ }}{2} = \frac{9 - 4}{2} = 2.5$