What by-products result from the combustion of hydrocarbon fuels aside from heat?

When hydrocarbons are combusted, the primary by-products are carbon dioxide (CO2) and various pollutants. This is because hydrocarbons are primarily composed of carbon and hydrogen; when they burn in the presence of oxygen, they mainly produce water vapor (H2O) and carbon dioxide. The complete combustion of hydrocarbons ideally results in just these two products. However, due to factors such as incomplete combustion, the conditions under which the fuel burns, and the type of fuel being used, additional pollutants can be formed.

These pollutants often include unburned hydrocarbons, carbon monoxide (CO), particulate matter, and nitrogen oxides (NOx), which arise from the high temperatures involved in the combustion process. This underlines the complex nature of combustion where not only the intended products are generated but also a variety of harmful substances that contribute to air pollution and climate change.

In contrast to the other choices, which either limit the products to a narrower range or focus solely on one type of by-product, the selected answer accurately reflects the broader spectrum of emissions produced during hydrocarbon combustion, particularly highlighting the formation of both carbon dioxide and other pollutants.