Elementary Reactions Practice Test

A researcher proposes the following elementary gas-phase step:

$$\text{CO}(g)+\text{Cl}_2(g)\rightarrow \text{COCl}_2(g)$$

Which rate law must apply if the step is elementary?

In an aqueous solution, the following elementary step is proposed:

$$\text{H}^+(aq)+\text{OH}^-(aq)\rightarrow \text{H}_2\text{O}(l)$$

Using the definition of an elementary step, which rate law is correct for this reaction?