Final answer:
The ratio of aluminum ions to oxygen ions in Al2O3, which is aluminum oxide, is 2:3 to maintain electrical neutrality, as 2 aluminum ions (each with a 3+ charge) balance with 3 oxygen ions (each with a 2- charge).
Step-by-step explanation:
The ratio of aluminum ions to oxygen ions in Al2O3 must result in an electrically neutral compound. Since aluminum has a charge of 3+ and oxygen has a charge of 2-, two aluminum ions (2 x 3+ = 6+) will balance with three oxygen ions (3 x 2- = 6-) to maintain neutrality. Therefore, the ratio of aluminum ions to oxygen ions in Al2O3 is 2:3.