Which gas is colorless, odorless, highly poisonous and formed by incomplete combustion of carbon or carbon material including gasoline?

• A. Carbon dioxide
• B. Cyanosis
• C. Carbon monoxide
• D. Decompose

Answer: (C)

Incomplete combustion of carbon-based fuels can produce carbon monoxide, a gas that is both colorless and odorless and highly poisonous. The danger lies in how CO affects the blood: it binds to hemoglobin with a much higher affinity than oxygen, forming carboxyhemoglobin. This not only reduces the blood’s ability to carry oxygen, but it also makes it harder for oxygen to be released to tissues, leading to tissue hypoxia. This is especially dangerous in enclosed spaces where engines or heaters run, because you may not notice any warning signs.

Carbon dioxide is also a gas produced by combustion, but it is not typically described as highly poisonous in normal exposure levels, and it doesn’t bind to hemoglobin the way CO does. Cyanosis is a symptom (bluish discoloration) of inadequate oxygen, not a gas itself. “Decompose” isn’t a gas and doesn’t fit the description.