Question

which of these is a harmful pollutant released by combustion?
carbon monoxide
chlorine
nitrogen
formaldehyde

Explanation:

Carbon - monoxide is a common harmful pollutant released during incomplete combustion. Chlorine is not typically a product of common combustion processes. Nitrogen is a major component of air and is not a harmful pollutant released by combustion in normal circumstances. Formaldehyde is not a primary product of most combustion reactions.

Answer:

carbon monoxide