Hydrogen chloride (HCl) is a significant compound with various physical and chemical properties. Physically, it is a colorless gas with a pungent odor and is highly soluble in water, leading to the formation of hydrochloric acid, which is a strong acid. Chemically, HCl exhibits noteworthy behavior, such as turning moist blue litmus paper red, indicating its acidic nature. It reacts vigorously with metals, carbonates, and oxides to yield salts. Notably, when hydrogen chloride comes into contact with ammonia (NH₃), it produces ammonium chloride (NH₄Cl), visible as white fumes. This section emphasizes the critical role HCl plays in many industrial and laboratory processes.