Explanation

(a)
$O_{2} = 8 + 8 = 16$
= $\sigma 1s^{2},\ _{\sigma}^{*}1s^{2}\ ,\sigma 2s^{2},\ _{\sigma}^{*}2s^{2}\ ,\ \sigma 2p_{z}^{2},(\pi 2p_{x}^{2} = \pi 2p_{y}^{2}),{(\ }_{\pi}^{*}2p_{x}^{1} = \ _{p}^{*}2p_{y}^{1})$
$\because$ It has 2 unpaired electrons.
$\therefore$ It is paramagnetic.
$CN^{-} = 6 + 7 + 1 = 14$
=$\ \sigma 1s^{2},\ _{\sigma}^{*}1s^{2}\ ,\sigma 2s^{2},\ _{\sigma}^{*}2s^{2}\ ,\ \sigma 2p_{z}^{2},(\pi 2p_{x}^{2} = \pi 2p_{y}^{2})$
$\therefore$ No unpaired electron and no paramagnetic.
$CO = 6 + 8 = 14$
=$\ \sigma 1s^{2},\ _{\sigma}^{*}1s^{2}\ ,\sigma 2s^{2},\ _{\sigma}^{*}2s^{2}\ ,\ \sigma 2p_{z}^{2},(\pi 2p_{x}^{2} = \pi 2p_{y}^{2})$
$\therefore$ No unpaired electron and no paramagnetic.
$NO^{+} = 7 + 8 - 1 = 14$
=$\ \sigma 1s^{2}\ _{\sigma}^{*}1s^{2}\ ,\sigma 2s^{2},\ _{\sigma}^{*}2s^{2}\ ,\ \sigma 2p_{z}^{2},(\pi 2p_{x}^{2} = \pi 2p_{y}^{2})$
$\therefore$ No unpaired electron and not paramagnetic.