The reaction between a reactive metal and an excess of a dilute acid is studied. The total volume of hydrogen gas formed is measured at intervals of $30$ seconds over a period of $3$ minutes. The mean rate of reaction in the first $30$ seconds is $P$. The mean rate of reaction in the final $30$ seconds is $Q$. What is the value of $P - Q$?
- A$1.21\ \text{cm}^3\ \text{s}^{-1}$
- B$1.93\ \text{cm}^3\ \text{s}^{-1}$
- C$2.13\ \text{cm}^3\ \text{s}^{-1}$
- D$3.43\ \text{cm}^3\ \text{s}^{-1}$