Which of the following best explains the accumulation of gas in one of the inverted test tubes during a gas evolution reaction?

• A. Evaporation of water led to the formation of water vapor in the test tube.
• B. The test tube was not properly sealed, allowing atmospheric air to enter.
• C. A chemical reaction produced a gaseous product that displaced water in the test tube.
• D. The test tube was heated, causing the air inside to expand and fill the tube.

Answer: (C)

Verified step by step guidance

1. Understand that in a gas evolution reaction, a chemical reaction produces a gas as one of its products.
2. Recognize that when a gas is produced in a reaction occurring in an inverted test tube filled with water, the gas will displace the water because gases occupy space and push the liquid out.
3. Evaluate the other options: evaporation of water produces water vapor but typically not enough to cause significant accumulation; improper sealing would allow air in but not cause gas accumulation from the reaction itself; heating air causes expansion but does not produce new gas.
4. Conclude that the accumulation of gas in the test tube is best explained by the chemical reaction generating a gaseous product that pushes the water out, leading to visible gas collection.
5. Summarize that gas evolution reactions are identified by the formation of a gas that can be collected or observed as it displaces liquid in a container.