Explanation:
According to molecular orbital diagramelectronic configuration of.
$\begin{gathered}
\mathrm{NO}^{+}(14 \mathrm{e})-\sigma 1 \mathrm{~s}^2, \sigma^* 1 \mathrm{~s}^2, \sigma 2 \mathrm{~s}^2, \sigma^* 2 \mathrm{~s}^2, \pi 2 \mathrm{p}_{\mathrm{x}}^2=\pi 2 \mathrm{p}_{\mathrm{y}}^2, \sigma 2 \mathrm{p}_z^2, \\
\pi^* 2 \mathrm{p}_{\mathrm{x}}=\pi^* 2 \mathrm{p}_{\mathrm{y}} \\
\mathrm{NO}\left(15 \mathrm{e}^{-}\right)-\sigma 1 \mathrm{~s}^2, \sigma^* 1 \mathrm{~s}^2, \sigma 2 \mathrm{~s}^2, \sigma^* 2 \mathrm{~s}^2 \sigma 2 \mathrm{p}_z^2, \pi 2 \mathrm{p}_{\mathrm{x}}^2=\pi 2 \mathrm{p}_y^2, \pi^* 2 \mathrm{p}_{\mathrm{x}}^1=\pi^* 2 \mathrm{p}_y
\end{gathered}$
The last electron into $\pi^* 2 \mathrm{p}_{\mathrm{x}}$ orbital i.e. $\pi^*$ orbital.
