In the reaction between limestone powder(calcium carbonate) hydrochloric acid, 17 cm3 of carbon dioxide that produced is in 3.5 minutes.
Average rate of reaction is 17 cm3/3.5 min
But, during the second minute, only (12.5 - 7.5) cm3 of carbon dioxide gas released in 1 minute time,
Average rate of reaction during the second minute is
(12.5 - 7.5) cm3 / (2 - 1) min
The correct answer is : C