Which one of the following statements about the law of conservation of mass is correct?

The law of conservation of mass, formulated by Antoine Lavoisier, states that matter can neither be created nor destroyed in a chemical reaction [1]. This principle implies that the total mass of the reactants must equal the total mass of the products, as the number of atoms of each element remains constant throughout the process [1]. Option 1 describes the Law of Definite Proportions, which states that a compound always contains elements in a fixed ratio by mass [2]. Option 2 refers to Gay-Lussac’s Law of Gaseous Volumes, which notes that gases combine in simple whole-number ratios by volume at constant temperature and pressure. Option 4 describes Avogadro’s Law, stating that equal volumes of gases at the same temperature and pressure contain an equal number of molecules. Therefore, only statement 3 correctly defines the law of conservation of mass.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > 1.1.2 Balanced Chemical Equations > p. 3