Which of the following statements concerning molecular orbital theory is true?

• A. Antibonding molecular orbitals increase the bond order of a molecule.
• B. The number of molecular orbitals formed is always less than the number of atomic orbitals combined.
• C. Molecular orbitals are always localized between two atoms.
• D. Bonding molecular orbitals are lower in energy than the atomic orbitals from which they are formed.

Answer: (D)

Verified step by step guidance

1. Recall that molecular orbital (MO) theory describes how atomic orbitals combine to form molecular orbitals when atoms bond.
2. Understand that when atomic orbitals combine, they form an equal number of molecular orbitals; this means the number of MOs formed is always equal to the number of atomic orbitals combined, not less.
3. Recognize that bonding molecular orbitals are formed by constructive interference of atomic orbitals, which lowers the energy compared to the original atomic orbitals, stabilizing the molecule.
4. Know that antibonding molecular orbitals result from destructive interference and are higher in energy, which decreases the bond order if occupied.
5. Note that molecular orbitals can be delocalized over several atoms, so they are not always localized strictly between two atoms.