Final answer:
The formula unit for a compound made from Fe3+ and oxygen is Fe2O3, which is also known as iron (III) oxide.
Step-by-step explanation:
The formula unit for a compound made from Fe3+ and oxygen is Fe2O3. This compound is known as iron (III) oxide and is an ionic compound. The formula signifies that there are two iron atoms for every three oxygen atoms. By determining the moles of each element and using the smallest whole number ratio, we can conclude that the empirical formula is Fe2O3.