Balance the equation: Fe + O2 → Fe2O3.

• A. Fe + O2 → Fe2O3
• B. 2 Fe + 3 O2 → 2 FeO3
• C. 4 Fe + 3 O2 → 2 Fe2O3
• D. 3 Fe + 2 O2 → Fe3O4

Answer: (C)

Balancing a chemical equation is all about conserving mass: the same number of each kind of atom must appear on both sides. For Fe reacting with O2 to form Fe2O3, assign coefficients to Fe, O2, and Fe2O3 and set up the atom counts: iron on the left must equal iron on the right, so the left coefficient for Fe must be twice the coefficient for Fe2O3. Oxygen must also balance: the left side has twice the O2 coefficient, while the right side has three oxygens per Fe2O3, so 2b = 3c. Choosing c = 2 gives b = 3 and iron coefficient a = 4. Put together, the balanced equation is 4 Fe + 3 O2 → 2 Fe2O3.

This keeps the product as the requested Fe2O3 and respects the conservation of both iron and oxygen. The other forms either change the product to a different oxide or fail to balance the atom counts, so they don’t match the given reaction.