Which statement best describes the main principle behind the law of conservation of mass?

• A. Energy is always conserved in every physical and chemical process.
• B. The total number of molecules always remains constant in a reaction.
• C. Atoms can be converted into energy during ordinary chemical reactions.
• D. Mass is neither created nor destroyed during a chemical reaction.

Answer: (D)

Verified step by step guidance

1. Understand that the law of conservation of mass states that in a chemical reaction, matter cannot be created or destroyed.
2. Recognize that this means the total mass of the reactants must equal the total mass of the products.
3. Note that this principle is fundamental to balancing chemical equations, ensuring the same number of atoms of each element on both sides.
4. Distinguish this from conservation of energy, which is a separate principle stating energy cannot be created or destroyed, only transformed.
5. Conclude that the correct statement is: 'Mass is neither created nor destroyed during a chemical reaction,' as it directly reflects the law of conservation of mass.