Final answer:
The normal percentages of oxygen and carbon dioxide in the flue gas of a properly operating gas furnace are approximately 16% and 4%, respectively, which indicates efficient combustion. The correct answer is B) 16% oxygen, 4% carbon dioxide.
Step-by-step explanation:
The normal oxygen and carbon dioxide percentages in the flue gas of a properly operating gas furnace are important to ensure efficient burning and to minimize harmful emissions. Atmospheric air, which is used for combustion, consists of approximately 20.9% oxygen, and only 0.04% carbon dioxide. During combustion in a gas furnace, oxygen is consumed while carbon dioxide is produced. A well-adjusted furnace typically has a flue gas composition with about 16% oxygen and around 4% carbon dioxide, which indicates that there is enough oxygen for the fuel to burn completely, turning into carbon dioxide and water vapour. Therefore, the correct answer to the student's question is B) 16% oxygen, 4% carbon dioxide.