Which of the following best states the law of conservation of mass?

• A. Energy is always conserved during physical and chemical changes.
• B. Mass is neither created nor destroyed in a chemical reaction.
• C. The total number of atoms increases during a chemical reaction.
• D. Matter can be converted entirely into energy in ordinary chemical reactions.

Answer: (B)

Verified step by step guidance

1. Understand that the law of conservation of mass states that in any chemical reaction, the total mass of the reactants equals the total mass of the products.
2. Recognize that this means mass cannot be created or destroyed during a chemical reaction, only rearranged.
3. Evaluate each option by comparing it to this principle: the correct statement must reflect that mass remains constant.
4. Note that the option 'Mass is neither created nor destroyed in a chemical reaction' directly expresses the law of conservation of mass.
5. Conclude that the other options either refer to energy conservation, changes in atom numbers, or matter-energy conversion, which are not accurate descriptions of the law of conservation of mass.