Which one of the following molecules is expected to exhibit paramagnetic behaviour?

According to the Molecular Orbital Theory (MOT),

For $$O_2$$ (16 electrons):

The configuration is $$\sigma1s^2, \sigma^*1s^2, \sigma2s^2, \sigma^*2s^2, \sigma2p_z^2, (\pi2p_x^2 = \pi2p_y^2), (\pi^*2p_x^1 = \pi^*2p_y^1)$$

Oxygen has two unpaired electrons in the degenerate antibonding $$\pi^*$$ orbitals. Thus, it is paramagnetic.

For $$O_2^{2-}$$ (Peroxide ion, 18 electrons):

The configuration is $$\sigma1s^2, \sigma^*1s^2, \sigma2s^2, \sigma^*2s^2, \sigma2p_z^2, (\pi2p_x^2 = \pi2p_y^2), (\pi^*2p_x^2 = \pi^*2p_y^2)$$

All electrons are paired. Thus, it is diamagnetic.

For $$C_2$$ (12 electrons):

The configuration is $$\sigma1s^2, \sigma^*1s^2, \sigma2s^2, \sigma^*2s^2, (\pi2p_x^2 = \pi2p_y^2)$$

All electrons are paired. Thus, it is diamagnetic.

For $$N_2$$ (14 electrons):

The configuration is $$\sigma1s^2, \sigma^*1s^2, \sigma2s^2, \sigma^*2s^2, (\pi2p_x^2 = \pi2p_y^2), \sigma2p_z^2$$

All electrons are paired. Thus, it is diamagnetic.