In chemical reactions, which law states that matter is neither created nor destroyed?

• A. Boyle's Law
• B. Law of Definite Proportions
• C. Law of Conservation of Energy
• D. Law of Conservation of Mass

Answer: (D)

Mass cannot be created or destroyed in a chemical reaction; the atoms are just rearranged to form new substances, so the total amount of matter stays the same in a closed system. This principle is what you use when you balance chemical equations—the same number of each type of atom must appear on both sides, guaranteeing that mass is conserved from reactants to products. The other statements describe different ideas: one is about how gases behave with pressure and volume, another about a compound having a fixed composition by mass, and the last about energy conservation. In the context of matter in chemical changes, the conservation of mass is the guiding rule.