Hydrogen sulfide (H₂S) is an inorganic compound that, under standard conditions, is a flammable, colorless gas with a pungent odor of rotten eggs at low concentrations. It is highly toxic, with a sulfur smell at extremely low concentrations. The aqueous solution of H2S is known as hydrosulfuric acid, a weak acid that is stronger than boric acid but weaker than carbonic acid. It is soluble in water, alcohols, petroleum solvents, and crude oil. Hydrogen sulfide is an essential chemical raw material used in various applications such as manufacturing synthetic phosphors, electroluminescent materials, photoconductors, and photoelectric exposure meters. It serves as a reducing agent in organic synthesis, refining metals, producing pesticides and pharmaceuticals, and regenerating catalysts. It is also used in preparing various sulfides and inorganic sulfides, identifying metal ions in chemical analysis, and producing high-purity hydrogen sulfide for semiconductor applications. Additionally, it is a critical raw material for infrared optical materials and is used in defense, chemical industries, and as an intermediate for pharmaceuticals and pesticides.