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Question

When 16 g of oxygen is combined with 2 g of hydrogen, 18 g water is formed. This observation is in accordance with:

This question was previously asked in
RRB Group D 2025 Question Paper (9-Aug-2026) (Shift 1)
The correct answer is

law of conservation of mass

The law of conservation of mass, stated by Antoine Lavoisier, says that in any chemical reaction the total mass of the reactants equals the total mass of the products.

Here, 2 g of hydrogen + 16 g of oxygen = 18 g, which is exactly the mass of the water produced, so no mass is created or destroyed.

The law of multiple proportions and Gay-Lussac’s law concern ratios of masses or volumes across different compounds/reactions, and Avogadro’s law relates equal volumes of gases to equal molecules, none of which is what is being demonstrated.

Hence, the observation obeys the law of conservation of mass.

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