Which of the following is NOT a component of flue gases from natural gas combustion?

The correct answer highlights that carbon monoxide, while a byproduct of incomplete combustion, is indeed a component of flue gases from natural gas combustion. When natural gas combusts, the primary products are normally carbon dioxide, water vapor, and nitrogen. However, in conditions where there is insufficient oxygen or when combustion is not perfect, carbon monoxide can be produced. This makes it a potential component, albeit an undesirable one, in flue gases.

In contrast, oxygen is typically found in the flue gas as well, albeit in smaller quantities than in the incoming air, as some oxygen remains unreacted after the combustion process. Water vapor is another significant product generated during the combustion of natural gas, as it results from the combination of hydrogen in the gas with oxygen from the air. Nitrogen, being a major component of the atmosphere, is also present in flue gases primarily because it does not react during the combustion process and hence enters and exits with the combustion products.

Understanding the role and presence of each of these components in natural gas combustion is crucial for evaluating combustion efficiency and safety, and managing ventilation systems effectively.