Final answer:
Bonding and antibonding molecular orbitals are formed simultaneously when two atomic orbitals combine according to molecular orbital theory. Bonding orbitals have lower energy and add stability, while antibonding orbitals have higher energy and contribute to instability, regardless of electron presence.
Step-by-step explanation:
According to molecular orbital theory, when two atomic orbitals combine, they form bonding and antibonding molecular orbitals. The correct statement about these orbitals is that bonding and antibonding orbitals exist simultaneously.
This occurs because when atomic orbitals overlap, one molecular orbital will result in constructive interference (in-phase combination), which leads to a lower energy bonding orbital. Concurrently, a higher energy antibonding orbital is created from destructive interference (out-of-phase combination).
Furthermore, the resulting bonding molecular orbital has a lower energy than the original atomic orbitals, thus providing stability to the molecule as it allows for the filling of electrons. In contrast, the antibonding molecular orbital has a higher energy than the original atomic orbitals and usually remains empty or less filled as it is less stable. Therefore, the existence of these orbitals is not dependent on the presence of electrons; they exist inherently upon the combination of atomic orbitals.