Final answer:
A molecule with an even number of electrons can be paramagnetic if it has unpaired electrons, according to molecular orbital theory. However, if all the electrons in the molecule are paired, it is always diamagnetic.
Step-by-step explanation:
Materials with unpaired electrons are paramagnetic and attracted to a magnetic field, while those with all-paired electrons are diamagnetic and repelled by a magnetic field. In molecular orbital theory, electrons fill molecular orbitals following the same rules as filling atomic orbitals.
Hund's rule and the Aufbau principle state that lower-energy orbitals fill first, electrons spread out before pairing up, and each orbital can hold a maximum of two electrons with opposite spins. Therefore, if a molecule with an even number of electrons has unpaired electrons, it can be paramagnetic. However, if all the electrons are paired, it is always diamagnetic.