How is carbon monoxide primarily formed?

Carbon monoxide is primarily formed through the incomplete combustion of carbon-containing fuels. This occurs when there is insufficient oxygen present during the burning process, leading to the production of carbon monoxide instead of carbon dioxide. Common sources of carbon monoxide include vehicles, gas appliances, and industrial processes where carbon fuels, such as gasoline, natural gas, wood, or coal, are burned.

This understanding highlights the importance of ensuring proper ventilation and oxygen supply in environments where combustion occurs to prevent the buildup of carbon monoxide, which can be harmful or even deadly to humans. The other processes listed do not primarily contribute to the formation of carbon monoxide, as they either involve complete combustion or natural occurrences that do not directly lead to this toxic gas.