Which of the following scenarios best illustrates the law of conservation of mass?

• A. A sealed container in which hydrogen gas reacts with oxygen gas to form water, and the total mass before and after the reaction remains the same.
• B. A reaction in an open flask where the mass increases after the reaction due to absorption of moisture from the air.
• C. A process where the mass of the reactants is greater than the mass of the products because some matter is destroyed.
• D. A container where a chemical reaction occurs and the mass of the products is less than the mass of the reactants due to gas escaping.

Answer: (A)

Verified step by step guidance

1. Understand the law of conservation of mass, which states that mass cannot be created or destroyed in a chemical reaction; the total mass of reactants must equal the total mass of products.
2. Analyze each scenario to see if the total mass before and after the reaction remains constant, considering whether the system is closed or open.
3. Recognize that in a sealed container, no matter can enter or leave, so the mass of reactants and products should be the same, illustrating the law correctly.
4. Identify that scenarios involving open systems where mass changes due to gas escaping or moisture absorption do not demonstrate the law properly because mass is not conserved within the system boundaries.
5. Conclude that the scenario with a sealed container where hydrogen and oxygen react to form water, and the total mass remains unchanged, best illustrates the law of conservation of mass.