Which law states that mass is neither created nor destroyed in a chemical reaction?

The law that states that mass is neither created nor destroyed in a chemical reaction is the Law of Conservation of Mass. This fundamental principle, established by Antoine Lavoisier in the 18th century, asserts that the total mass of substances involved in a chemical reaction remains constant, meaning that the mass of the reactants equals the mass of the products. This concept is critical to the understanding of chemical equations and stoichiometry, as it implies that atoms are simply rearranged during a reaction, rather than lost or gained.

Other options mention different scientific principles that are unrelated to the conservation of mass. For example, the Law of Diminishing Returns pertains to economics and the productivity of inputs, while the Law of Conservation of Energy relates to the interchangeability of energy forms, highlighting that energy cannot be created or destroyed but can be transformed from one form to another. The Law of Definite Proportions refers to the fact that a chemical compound always contains its component elements in fixed ratio by mass, but does not address the conservation of mass concept.