Option C is correct because when the x-axis is the internuclear axis, the overlap of $2p_y$ and $2p_y$ orbitals results in a pi ($\pi$) bond, not a sigma ($\sigma$) bond. Sigma molecular orbitals are symmetrical around the bond-axis, whereas pi molecular orbitals are not symmetrical. The $2p_y$ orbitals have positive lobes above and negative lobes below the molecular plane, making them unsuitable for sigma bonding along the x-axis.