Which gas has a smell reminiscent of rotten eggs, is toxic, and often found in sewage facilities?

The gas that has a smell reminiscent of rotten eggs, is toxic, and is commonly found in sewage facilities is hydrogen sulfide. This gas is produced during the breakdown of organic materials in the absence of oxygen, which frequently occurs in sewage systems and other confined spaces where organic waste is present.

Hydrogen sulfide is dangerous because it can cause serious health effects upon exposure, including respiratory distress and even death in high concentrations. Its distinct odor serves as a warning sign; however, at very high levels, individuals may lose their sense of smell, which can lead to dangerous situations if proper precautions are not in place.

In contrast, carbon dioxide is typically odorless and does not have the same toxic properties as hydrogen sulfide, although it can be harmful in high concentrations. Sulfur dioxide, while also having an unpleasant smell, is most commonly associated with industrial processes such as combustion and is not primarily found in sewage facilities. Methane is another odorless gas that is often present in sewage environments; however, it does not have the rotten egg smell that hydrogen sulfide does and poses different risks, primarily related to flammability.