What does the Conservation Law of mass state?

• A. Mass is conserved in closed systems
• B. Mass can be created or destroyed in chemical reactions
• C. Energy is always conserved
• D. Mass increases with chemical reaction

Answer: (A)

The main idea being tested is that mass stays the same in a closed system during a chemical change. In a sealed container, the total amount of matter doesn’t disappear or appear; atoms are just rearranged to form new substances. The reactants’ masses equal the products’ masses because the same atoms are present before and after the reaction, even though they bond differently.

If the system truly stays closed, weighing the whole setup before and after the reaction gives the same total mass, despite visible changes in what’s inside. The idea is not about energy—energy can change forms, but mass itself remains conserved in this context. If some material can escape the system, the mass inside the container might change, but the total mass of the entire surroundings remains constant.