Explain why the mass of the products equals the mass of the reactants in a chemical reaction.

The mass of the products equals the mass of the reactants because, according to the law of conservation of mass, atoms are neither created nor destroyed in a chemical reaction. Therefore, the total mass remains constant throughout the reaction.

This answer effectively explains the relationship between reactants and products in terms of mass conservation, demonstrating understanding of the concept. The question assesses the student's ability to explain a fundamental principle in chemistry.