Explanation

(c)
$RbO_{2}$ means $Rb^{+}$ and $0_{2}^{-},\ 0_{2}^{-}$ is the superoxide ion.
$0_{2}^{-}(17) = \sigma 1s^{2},\ _{\sigma}^{*}1s^{2}\ ,\sigma 2s^{2},\ _{\sigma}^{*}2s^{2},\sigma 2p_{z}^{2}\ ,\ \pi 2p_{x}^{2} \approx \pi 2p_{y,}^{2}\ _{\pi}^{*}2p_{x,}^{2} \approx \ _{\pi}^{*}2p_{y}^{1}$
As it contains one unpaired electron, thus paramagnetic in nature.$\$