What does the Law of Mass Conservation state?

• A. Energy cannot be created or destroyed
• B. Matter cannot be created or destroyed; it can only change forms
• C. Atoms cannot be divided
• D. The mass of a chemical reaction is always less than the mass of reactants

Answer: (B)

The main concept tested is that during a chemical change, matter is conserved: the total amount of mass doesn’t change, it just changes form. In a closed system, atoms are simply rearranged to form new substances, so the total mass of the products equals the total mass of the reactants. This is why mass is conserved even though substances may transform, combine, or separate.

That’s why the best choice says matter cannot be created or destroyed; it can only change forms. The other ideas don’t fit: energy conservation is a different principle (energy, not mass, is conserved in general); atoms can be divided in some processes (especially nuclear reactions), so the statement that atoms cannot be divided isn’t accurate for all contexts; and the mass of a chemical reaction is not less than the mass of the reactants—mass is conserved.