Final answer:
The correct formula for aluminum oxide is Al2O3, which reflects the 2:3 ratio of aluminum ions to oxide ions needed to balance the charges and achieve an electrically neutral compound.
Step-by-step explanation:
The formula for aluminum oxide is Al2O3. This compound is formed when aluminum ions Al3+ combine with oxide ions O2- in a ratio that balances the overall charge of the compound, making it electrically neutral. Each aluminum ion has a +3 charge and each oxide ion has a -2 charge. To achieve neutrality, two aluminum ions (for a total of +6 charge) combine with three oxide ions (for a total of -6 charge), resulting in the formula Al2O3. Therefore, the correct answer is A. Al2O3.