Which characteristic of hydrogen sulfide makes it dangerous?

Hydrogen sulfide is dangerous primarily because it is both flammable and poisonous. As a colorless gas, it has a distinct rotten egg odor at low concentrations, but its smell can quickly become imperceptible at higher levels, which poses a significant risk as people may be unaware of its presence.

The flammability of hydrogen sulfide means it can easily ignite when mixed with air in certain concentrations, presenting fire hazards in environments where the gas may accumulate. Furthermore, it is highly toxic; even exposure to low concentrations can lead to serious health issues or fatalities. It directly impacts the respiratory system and can cause symptoms ranging from irritation of the eyes and throat to more severe effects like loss of consciousness at higher exposure levels.

Understanding these properties emphasizes the need for safety precautions when handling or working in environments where hydrogen sulfide may be present. In contrast, the other characteristics listed do not apply to hydrogen sulfide, highlighting why they do not represent its dangers.