Final answer:
a) Constructive interference, increased
Atomic orbitals that combine with constructive interference create a bonding molecular orbital with increased electron density, which stabilizes the molecule and is lower in energy compared to the atomic orbitals from which it was derived.
Step-by-step explanation:
Atomic orbitals combine in different ways to form molecular orbitals, which can either be bonding or antibonding depending on the nature of the interference of the wave functions from which they derive. When atomic orbitals combine with constructive interference, the result is an increase in electron density between the nuclei.
This results in a bonding molecular orbital that stabilizes the molecule. Conversely, destructive interference between atomic orbitals leads to a decrease in electron density and the formation of an antibonding molecular orbital, which is higher in energy and destabilizes the molecule.
Therefore, the answer to the student's question is: Atomic orbitals combining with constructive interference produce a bonding molecular orbital - a region of increased electron density that exists between the nuclei. The correct option is a) Constructive interference, increased.