According to the Law of Conservation of Mass, what is always true about the total amount of O_2 and CO_2 in a closed test tube during a chemical reaction?

• A. The combined mass of O_2 and CO_2 remains constant throughout the reaction.
• B. The mass of CO_2 is always greater than the mass of O_2.
• C. The total mass of O_2 and CO_2 increases as the reaction proceeds.
• D. The mass of O_2 always decreases while the mass of CO_2 increases.

Answer: (A)

Verified step by step guidance

1. Recall the Law of Conservation of Mass, which states that mass cannot be created or destroyed in a closed system during a chemical reaction.
2. Identify that in a closed test tube, no substances can enter or leave, so the total mass of all substances inside remains constant.
3. Recognize that O_2 and CO_2 are two substances involved in the reaction, and their combined mass must remain the same throughout the reaction.
4. Understand that while the individual masses of O_2 and CO_2 may change (O_2 might decrease as it reacts, CO_2 might increase as it forms), their total combined mass does not change.
5. Conclude that the correct statement is: the combined mass of O_2 and CO_2 remains constant throughout the reaction, consistent with the Law of Conservation of Mass.