In a pseudo first order reaction, [A]/mol L^-1 reads 0.31 at t = 30 s and 0.17 at t = 60 s. What is the average rate of reaction over this interval in mol L^-1 s^-1?

1. Average rate $= -\dfrac{\Delta[A]}{\Delta t}$. 2. $\Delta[A] = 0.17 - 0.31 = -0.14\ \text{mol L}^{-1}$ over $\Delta t = 60 - 30 = 30\ \text{s}$. 3. Rate $= \dfrac{0.14}{30} = 4.7\times10^{-3}\ \text{mol L}^{-1}\text{s}^{-1}$. 4. Distractor D forgets to divide by the time interval; distractor C halves the result. _Source: NCERT Class 12 Chemistry Ch 3 "Chemical Kinetics", p.24_