half the reaction means half the calcium carbonate to react and therefore half of 90 i-e 45 cm cube of CO2 is produced and so the corresponding time………………..

You are Spot On! Your approach is correct.

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This is a common error made by many students.

Please note that Since half of the carbonate is used, total volume of CO2 produced will be halved.

Answer should be A for this question.

PS: Do note that the amount of CO2 produced is NOT proportional to the reaction time.

Let me know if you have further questions.

Your concepts is correct. Since half of the carbonate is used, total volume of CO2 produced will be halved.

Answer should be A. Seems like you made an error while reading off the axes of the graph.

Hope this helps.

Since 90 cm3 is the total volume of gas evolved, half of it would be 45 cm3, and reading from the graph, it is about 0.95 mins.