Hydrogen sulfide is a toxic gas that smells like ______. At high concentrations, however, the sense of smell is deadened

• A. Dead fish
• B. Fuel gas
• C. Rotten cabbage
• D. Rotten eggs

Answer: (D)

Hydrogen sulfide has a distinct rotten-egg odor at low concentrations. But as the concentration increases, olfactory fatigue sets in and you stop detecting the smell, even though the gas is present and dangerous. That’s why rotten eggs is the best descriptor here—the odor is detectable only at safer, lower levels, while at higher levels you won’t smell it but the gas can still cause harm. In practice, don’t rely on smell to judge safety; use proper gas detectors and ventilation, since H2S can accumulate in low-lying areas and overwhelm you quickly.