Which constituent of smoke acts as an asphyxiate due to its narcotic nature?

Carbon monoxide is a colorless, odorless gas that is a byproduct of incomplete combustion. It acts as an asphyxiate primarily due to its ability to bind with hemoglobin in the blood, which prevents the blood from carrying oxygen to the body's tissues and organs. Its narcotic effects can impair the central nervous system, leading to dizziness, confusion, and even loss of consciousness. This makes it particularly dangerous in fire situations, where smoke and toxic gases can accumulate quickly.

In contrast, while carbon dioxide is also a byproduct of combustion and can contribute to asphyxiation at higher concentrations, it primarily displaces oxygen in the air rather than acting narcotically. Nitrogen, being an inert gas in this context, does not have any asphyxiating properties, and soot is not a gas but rather particulate matter that does not interfere with oxygen transport in the blood. Thus, carbon monoxide's specific properties make it the correct choice for indicating a narcotic asphyxiant in smoke.