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