Final answer:
To form one formula unit of the compound Al2 O3, a total of six electrons must be transferred.
Step-by-step explanation:
Because the ionic compound must be electrically neutral, it must have the same number of positive and negative charges. Two aluminum ions, each with a charge of 3+, would give us six positive charges, and three oxide ions, each with a charge of 2-, would give us six negative charges. The formula would be Al2O3.