Match each observation in List-I with the overall order of reaction in List-II that it shows. List-I (P) For a reaction of one reactant, the half-life falls from $40.0\ \text{min}$ to $20.0\ \text{min}$ when the starting concentration is doubled. (Q) The rate constant has the unit $\text{L}^{1/2}\ \text{mol}^{-1/2}\ \text{s}^{-1}$. (R) For rate $= k[\text{A}]^x[\text{B}]^y$, doubling $[\text{A}]$ alone makes the reaction 4 times faster, and doubling both $[\text{A}]$ and $[\text{B}]$ makes it 8 times faster. (S) For a reaction of one reactant, 75 per cent is used up in exactly twice the time taken for 50 per cent, whatever the starting concentration. List-II (1) 0 (2) 1 (3) 3/2 (4) 2 (5) 3