Final answer:
The correct formula for the compound formed from Al and O is Al2O3.
Step-by-step explanation:
The correct formula for a compound formed from the elements Al and O is Al2O3.
Because there is one octahedral hole per anion (oxide ion) and only two-thirds of these holes are occupied, the ratio of aluminum to oxygen must be 3:1, which would give Al2/3O. The simplest whole number ratio is 2:3, so the formula is Al2O3.