Which of the following is not considered a simple asphyxiant?

A simple asphyxiant refers to a substance that displaces oxygen in the air, leading to a reduced concentration of oxygen available for respiration. In this context, carbon monoxide is classified as a toxic gas rather than a simple asphyxiant because it interferes with the body's ability to transport oxygen. It binds with hemoglobin in red blood cells more effectively than oxygen, thus preventing oxygen from being delivered to tissues and organs, resulting in oxygen deprivation.

On the other hand, air, nitrogen, and helium are all considered simple asphyxiants because they can displace oxygen in the environment without directly causing harm through chemical toxicity. When these gases are present in high concentrations, they can reduce the oxygen levels in the air, leading to asphyxiation. Therefore, recognizing carbon monoxide's unique toxicological properties helps differentiate it from simple asphyxiants.