in any chemical reaction, the total mass of products is always equal to that of the reactants. This Is statement of the law of:

Step 1: Analyze the question The statement says that in any chemical reaction, the total mass of the products equals the total mass of the reactants. We need the law that describes this.

Step 2: Explain the concept This is the Law of Conservation of Mass (also called the Law of Conservation of Matter), stated by Antoine Lavoisier. It says matter can neither be created nor destroyed in a chemical reaction. Atoms are only rearranged, so the total mass stays the same.

Let's compare it with the other laws:

• Constant composition / Definite proportions (B, C): A pure compound always contains the same elements in the same proportion by mass (Proust). For example, water is always 1 part hydrogen to 8 parts oxygen by mass.
• Multiple proportions (D): When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in a simple whole-number ratio (Dalton). For example, CO and CO₂.
• Reciprocal proportions (E): If two elements each combine with a third element, the ratio in which they combine with each other is related to the ratios in which they combine with the third (Richter).

Step 3: Apply it Example: 2H₂ + O₂ → 2H₂O

• Reactants: 4 g of H₂ + 32 g of O₂ = 36 g
• Product: 36 g of H₂O

The mass is the same before and after, which matches the statement in the question.

Step 4: Answer The statement describes the law of conservation of matter (mass), which is option A.

Exam tip: Think "Conservation = Count the mass before and after." If a question talks about total mass before and after a reaction, it is conservation. If it talks about fixed ratios in a compound, it is definite proportions or constant composition. If it talks about different compounds of the same elements, it is multiple proportions.