Which statement best describes the principle of conservation of mass?

The principle of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. This fundamental concept, established by Antoine Lavoisier in the 18th century, underscores that the total mass of the reactants in a chemical reaction will always equal the total mass of the products.

In other words, when substances undergo a transformation during a reaction, the atoms that make up those substances are merely rearranged to form new substances; they do not vanish or appear from nowhere. This principle is crucial for understanding stoichiometry and balancing chemical equations, as it ensures that all atoms are accounted for in both the reactants and products.

The alternative options fail to accurately convey this principle. For instance, stating that mass can increase or is less in products than in reactants contradicts the foundational idea that mass remains constant throughout the reaction. Similarly, the incorrect assertion that mass can be lost as energy goes against the law; although energy can be transformed (as per Einstein's equation E=mc²), it does not violate the conservation of mass in typical chemical reactions.