Final answer:
C2 is a stable molecule with a bond order of 2 and it is diamagnetic, as determined from its molecular orbital diagram where all electrons are paired.
Step-by-step explanation:
Based on molecular orbital theory, the correct statement about C2 is that it is a stable molecule with a bond order of 2 and it is diamagnetic. The bond order of a molecule can be calculated from its molecular orbital diagram by subtracting the number of electrons in the antibonding orbitals from those in the bonding orbitals and then dividing by two. In the case of the diatomic molecule C2, both the 2s and 2p orbitals are involved in bonding, with the result that there are more electrons in bonding orbitals than in antibonding orbitals, leading to a bond order of 2. Additionally, since all electrons in C2 are paired, it exhibits diamagnetic properties, being repelled by a magnetic field.