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Question

In a chemical reaction, 12g of carbon reacts completely with 32g of oxygen to form carbon dioxide. If only 40g of carbon dioxide is collected, which of the following is the correct conclusion based on the Law of Conservation of Mass?

This question was previously asked in
RRB Group D 2025 Question Paper (18-Aug-2026) (Shift 1)
The correct answer is

Carbon dioxide gas escaped during the reaction, so mass was not fully collected.

By the Law of Conservation of Mass, mass is neither created nor destroyed in a chemical reaction: 12 g of carbon + 32 g of oxygen must together give 44 g of carbon dioxide. Since only 40 g of CO₂ was collected, the remaining 4 g of gas must have escaped during the reaction rather than being lost from existence.

Hence, this is the correct answer.

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