What defines a simple asphyxiant?

A simple asphyxiant refers specifically to a chemical that displaces oxygen in the atmosphere. This definition is crucial because it emphasizes the primary danger associated with simple asphyxiants: they reduce the amount of available oxygen necessary for human respiration. When these substances are present in high concentrations, they can cause symptoms ranging from lightheadedness to unconsciousness, and even death if oxygen levels become low enough.

Other choices do not accurately represent what constitutes a simple asphyxiant. For instance, a substance that enhances breathing would actually aid oxygen intake, whereas a simple asphyxiant does the opposite. A compound that condenses in water relates to solubility and does not pertain to the displacement of oxygen, and a gas that reacts violently with air refers to a different category of hazardous materials that can create explosive or toxic reactions, rather than simply decreasing the oxygen content in an environment. Thus, choice B is the only correct definition.