What are the gases that smell like rotten egg?

Gases that smell like rotten eggs are primarily hydrogen sulfide (H₂S) and, to a lesser extent, some sulfur compounds. Hydrogen sulfide is produced by the decomposition of organic matter, particularly in anaerobic environments. It is commonly found in sewage, swamps, and certain industrial processes. Exposure to high concentrations can be hazardous, so it's important to handle it with care.