Which of the following diatomic molecular species has only \( \pi \) bonds according to molecular orbital theory?

For \( \text{C}_2 \) (total 12 electrons), electronic configuration is \( \sigma 1s^2 \sigma^* 1s^2 \sigma 2s^2 \sigma^* 2s^2 \pi 2p_x^2 = \pi 2p_y^2 \), having two \( \pi \) bonds and no \( \sigma \) bonds in the valence shell.