Which of the following is the best example of the law of conservation of mass?

The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction [1]. Consequently, the total mass of the reactants must equal the total mass of the products [1]. In option 4, 12 gm of carbon (reactant) combines with 32 gm of oxygen (reactant) to produce 44 gm of carbon dioxide (product). Since 12 + 32 = 44, the mass is perfectly conserved during this chemical transformation. While options 1, 2, and 3 describe scenarios where mass remains constant, they represent physical states or inert conditions rather than a chemical reaction demonstrating the principle of mass conservation between different substances. Option 4 specifically illustrates the quantitative relationship defined by the law in a chemical context, making it the best example.

Sources

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