Consider the following reaction.

$${\text{2P}} + {\text{Q}} \to {\text{R}} + {\text{S}}$$

This reaction occurs according to the following mechanism.

$$\begin{array}{*{20}{l}} {{\text{P}} + {\text{Q}} \to {\text{X}}}&{slow} \\ {{\text{P}} + {\text{X}} \to {\text{R}} + {\text{S}}}&{fast} \end{array}$$

What is the rate expression?

A.     rate $= k{\text{[P]}}$

B.     rate $= k{\text{[P][X]}}$

C.     rate $= k{\text{[P][Q]}}$

D.     rate $= k{{\text{[P]}}^{\text{2}}}{\text{[Q]}}$

C