Gaseous nitrogen and gaseous hydrogen react in a rigid vessel to produce gaseous ammonia according to the balanced equation below.

\[\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightarrow 2\text{NH}_3\text{(g)}\]

A particulate representation of the initial reaction mixture in the vessel is shown in the diagram. If the reaction proceeds to completion, which of the following diagrams best represents the contents of the vessel after the reaction?