Which of the following fuels produces carbon monoxide (CO) when burned?

Natural gas, like the other listed fuels, can produce carbon monoxide (CO) when burned, particularly in conditions where there is insufficient oxygen for complete combustion. In a properly functioning furnace or appliance, natural gas typically burns cleanly to produce carbon dioxide and water. However, if the combustion process is disrupted—due to issues like inadequate ventilation, too high a carbon-to-hydrogen ratio, or poor burner adjustment—carbon monoxide can be a byproduct of this incomplete combustion.

Understanding the context of combustion reactions is crucial. While coal, propane, and wood can also yield carbon monoxide when burned, the scenario in which natural gas was selected indicates an aspect like its common use in household appliances where improper installation or maintenance could lead to CO production. Thus, while all these fuels can generate CO, the focus on natural gas may relate to its prevalence in consumer settings and the safety concerns surrounding its combustion, emphasizing the importance of ensuring proper ventilation and equipment maintenance to minimize carbon monoxide risks.