Balance the equation Fe + O2 -> Fe2O3.

• A. Fe + O2 -> Fe2O3
• B. 4 Fe + 3 O2 -> 2 Fe2O3
• C. 2 Fe + 3 O2 -> 2 Fe2O3
• D. 2 Fe + O2 -> Fe2O3

Answer: (B)

Balancing chemical equations means making sure the same number of atoms of each element are on both sides of the equation, reflecting conservation of mass. Fe2O3 has two iron atoms and three oxygen atoms in each formula unit. To form two units of Fe2O3, you need four iron atoms and six oxygen atoms. The six oxygens come from three O2 molecules (each O2 has two oxygens). Putting it together gives 4 Fe + 3 O2 -> 2 Fe2O3. This balance keeps both iron and oxygen counts equal on both sides. Options with fewer iron atoms or fewer O2 molecules don’t match the required counts, so they aren’t balanced.