Final answer:
The scene represents a mixture of A2 and B2 before they react to form AB3.
Step-by-step explanation:
The illustration describes a reaction mixture before the formation of a product AB3. The mixture initially contains molecules A2 (green) and B2 (blue). As the reaction progresses, A molecules decrease in number, while more B molecules are formed. This can be observed in the graph showing the change in the number of A and B molecules over time.