Which of the following diatomic molecular species has only $\mathrm{\pi }$ bonds according to Molecular Orbital Theory?

$B{e}_2\left(8\right):KK\sigma {\left(2s\right)}^2{\sigma }^{*}{\left(2s\right)}^2$

$O_2\left(16\right):KK\sigma \left(2s^2\right){\sigma }^{*}\left(2s^2\right)\sigma {\left(2p_z\right)}^2\pi {\left(2p_x\right)}^2\pi {\left(2p_y\right)}^2{\pi }^{*}{\left(2p_x\right)}^1{\pi }^{*}{\left(2p_y\right)}^1$

$N_2\left(14\right):KK\sigma {\left(2s\right)}^2{\sigma }^{*}{\left(2s\right)}^2\pi {\left(2p_x\right)}^2\pi {\left(2p_y\right)}^2\sigma {\left(2p_z\right)}^2$

$C_2\left(12\right):KK\sigma {\left(2s\right)}^2{\sigma }^{*}{\left(2s\right)}^2\pi {\left(2p_x\right)}^2\pi {\left(2p_y\right)}^2$

Therefore, $C_2$ contains $2\pi$ bonds as it has 4 electrons in two pi-molecular orbitals