Which of the following scientists formulated the law of conservation of mass?

Analyze the question: The question asks which scientist is credited with the law of conservation of mass. This law says that matter is neither created nor destroyed in a chemical reaction, so the total mass of the reactants equals the total mass of the products.

Explain the concept: Several scientists are linked to the early laws of chemistry, and the options mix them up on purpose:

• Antoine Lavoisier (1789): Law of Conservation of Mass. He carefully weighed substances before and after reactions in sealed vessels, and the mass stayed the same.
• John Dalton: Atomic Theory and the Law of Multiple Proportions. His theory explained why mass is conserved, because atoms are only rearranged and never created or destroyed. But he did not formulate the law itself.
• Robert Boyle: Boyle's Law (pressure and volume of a gas at constant temperature, P ∝ 1/V).
• Joseph Proust: Law of Definite (Constant) Proportions. A pure compound always contains the same elements in the same proportion by mass.

Solution, step by step:

1. The law in question is about mass being conserved in a reaction.
2. Dalton explained it with atomic theory but did not formulate it. Boyle is the gas law man. Proust is definite proportions.
3. That leaves Lavoisier, the "father of modern chemistry," who established the law through quantitative experiments.

Answer: A. A. Lavoisier

Exam tip: Match each scientist to one law:

• Lavoisier → Law of conservation of mass
• Proust → Proportions (definite)
• Dalton → Different (multiple) proportions and atoms
• Boyle → Balloon (gas pressure and volume)