Final answer:
The formula unit for the compound formed when Al³⁺ and CO₃²⁻ ions interact is Al₂(CO₃)₃.
Step-by-step explanation:
The formula unit for the compound formed when Al³⁺ and CO₃²⁻ ions interact is Al₂(CO₃)₃.
In this compound, the aluminum ion (Al³⁺) forms 2 ions with the carbonate ion (CO₃²⁻). To determine the formula unit, we need to balance the charges of the ions. Since aluminum has a charge of 3+ and carbonate has a charge of 2-, we need 2 aluminum ions to balance with 3 carbonate ions. Therefore, the formula unit is Al₂(CO₃)₃.