乙炔 (yǐxiàn), known as acetylene in English, is a colorless gas that is highly flammable. It is commonly used as a fuel in welding and cutting metals due to its high flame temperature. Acetylene is produced by the reaction of calcium carbide with water, making it an important industrial chemical. In addition to its use in welding, 乙炔 is also utilized in the synthesis of various organic compounds. It serves as a building block in the production of plastics, solvents, and other chemicals. Its unique properties make it valuable in both industrial and laboratory settings.