When aldehydes are present, carbon monoxide is ________.

When aldehydes are present, carbon monoxide is present as well. This is because aldehydes can form during the incomplete combustion of hydrocarbons, which is also a process that generates carbon monoxide. In environments where organic compounds are being burned, such as in combustion processes involving wood or fossil fuels, both aldehydes and carbon monoxide are common byproducts. Their presence indicates there may be incomplete oxidation occurring, which is a characteristic of combustion in conditions where oxygen supply is limited or not optimal. Understanding this relationship is crucial when evaluating combustion efficiency and emissions in various applications like fireplaces and other heating appliances.