Which compound is known to be highly toxic and competes with oxygen for binding sites?

The compound that is highly toxic and competes with oxygen for binding sites is carbon monoxide. Carbon monoxide binds to hemoglobin in red blood cells much more effectively than oxygen does. This binding prevents oxygen from attaching to hemoglobin, thereby reducing the amount of oxygen that can be transported in the bloodstream. This can lead to oxygen deprivation in tissues and result in serious health effects or even death.

In contrast, hydrogen sulfide, while also toxic, operates through different mechanisms, primarily affecting cellular respiration rather than directly competing with oxygen for binding sites on hemoglobin. Aspartame is an artificial sweetener and is not known for toxicity in the way carbon monoxide is, as it is generally recognized as safe for consumption. Acetylene is a flammable gas used primarily in welding and does not have the same competitive binding properties as carbon monoxide. Thus, carbon monoxide stands out as the specific compound that poses a risk by competing with oxygen for binding at critical sites in the body.