Answer:
The correct answer is B. Molecules of a compound.
Step-by-step explanation:
Carbon dioxide (CO2) is a compound composed of carbon and oxygen atoms chemically bonded together in a fixed ratio. In a compound, atoms of different elements are chemically combined in specific proportions, and the resulting substance has distinct properties different from the individual elements. Therefore, the combination of carbon and oxygen to form carbon dioxide is an example of molecules of a compound (option B).