Two reactions are run side by side at the same temperature, in separate flasks. X is zero order, so it is used up at a steady rate until none is left. Y is first order. Each reactant starts at $0.800\ \text{mol L}^{-1}$, and in these runs both have a half-life of $20.0\ \text{min}$. The graph shows the concentration of each reactant against time, with the two curves crossing at $20.0\ \text{min}$. Both runs are followed for $40.0\ \text{min}$. Take $\ln 2 = 0.693$. Which of the following statements are correct?

Fig. 1: A graph of concentration, in moles per litre, against time, in minutes, from 0 to 60 minutes. X, zero order, falls in a straight line from 0.800. Y, first order, falls along a curve from 0.800. The two cross at 20.0 minutes and 0.400 moles per litre, where a point is marked.