Final answer:
The mass of reactants in a chemical reaction is always equal to the mass of products, exemplifying the law of conservation of mass, which states matter cannot be created or destroyed.
Step-by-step explanation:
The question pertains to the relationship between the mass of reactants and products in a chemical reaction. According to the law of conservation of mass, the mass of the reactants should always equal the mass of the products. This fundamental principle indicates that matter, and therefore mass, cannot be created or destroyed in the course of a chemical reaction, but it can change forms (such as from solids to liquids or gases).
For example, in a balanced chemical equation, the number of atoms of each element in the reactants will be the same as that of the products. This demonstrates the law of conservation of mass. Accurate measurements and quantitative analyses of chemical reactions performed since the 1790s have reinforced the validity of this law.
Therefore, the correct answer to the question is D) The total mass of the products always equals the total mass of the reactants.