The time required for $90\%$ completion of a certain first order reaction is $1$ hour. Calculate the time required for $99.9\%$ completion of the same reaction.

The rate of the reaction $2A + 3B \rightarrow 2C + D$ is $6 \times 10^{-4} \text{ mol dm}^{-3}\text{ s}^{-1}$, when $[A] = [B] = 0.3 \text{ mol dm}^{-3}$. If the reaction is of first order for A and zeroth order for B, then find the rate constant.

What is the value of the slope of a graph obtained by plotting the concentration of reactant $(A)_t$ versus time for zero order reaction?

Which of the following nano structures includes nanotubes as an example?