What substance is an example of a chemical asphyxiant?

• A. Oxygen
• B. Carbon monoxide
• C. Nitrogen
• D. Helium

Answer: (B)

Chemical asphyxiants are substances that prevent the body's tissues from obtaining or using oxygen through a chemical interaction. Carbon monoxide is the classic example because it binds tightly to hemoglobin, forming carboxyhemoglobin. This dramatically reduces the blood’s capacity to carry oxygen and makes it harder for tissues to extract oxygen, leading to cellular hypoxia. The effect can occur even at low concentrations because CO competes with oxygen for binding sites and shifts the oxygen-hemoglobin balance in a way that impairs oxygen release to cells. Oxygen itself is essential and is not a chemical asphyxiant. Nitrogen and helium cause suffocation mainly by displacing air and lowering the ambient oxygen level, not by chemically interfering with oxygen transport or use.