Which gas is recognized by its rotten egg smell?

Hydrogen sulfide is known for its characteristic rotten egg smell, which is a result of its chemical composition. This gas is produced from the decay of organic matter and can be naturally found in places such as swamps or during the breakdown of sewage. The distinct odor serves as a warning sign of its presence, given that hydrogen sulfide is toxic and can be hazardous to health in high concentrations.

The other gases listed have different characteristics: methane is odorless, chlorine has a strong, pungent odor reminiscent of bleach, and ammonia has a sharp, somewhat irritating smell. Understanding these distinctions is crucial for safety and awareness when working with or around various gases.