Final answer:
The formula unit for a compound made from Fe₂ and oxygen is Fe₂O₃, which is the empirical formula for iron (III) oxide and reflects a 2:3 mole ratio of iron to oxygen atoms in the compound.
Step-by-step explanation:
The formula unit for a compound made from Fe₂ and oxygen is Fe₂O₃. This compound is known as iron (III) oxide, indicating that iron has an oxidation state of +3. To arrive at this formula, the ratio of moles of iron to oxygen is considered, which is 2 to 3. Since iron can have multiple oxidation numbers, in this case, the iron ion Fe³⁺ pairs with oxygen to create the ionic compound with the empirical formula Fe₂O₃. This represents the mole ratio of iron to oxygen in the compound and confirms it is composed of iron atoms and nonmetal oxygen atoms, which stick together due to ionic bonding.