Ammonium chloride (NH4Cl) is a white compound formed by the reaction of hydrogen chloride gas (HCl), an acid gas, and ammonia gas (NH3), a basic gas. When these two gases come into contact, they undergo a chemical reaction to form ammonium chloride according to the following equation:

HCl(g) + NH3(g) -> NH4Cl(s)

In this reaction, hydrogen ions (H+) from the HCl gas combine with hydroxide ions (OH-) from the NH3 gas to form water molecules (H2O), while the remaining ammonium cation (NH4+) and chloride anion (Cl-) combine to form ammonium chloride as a white solid.

Ammonium chloride is a water-soluble compound and readily dissolves in water to form ammonium (NH4+) and chloride (Cl-) ions, making it a common ingredient in various household and industrial applications. It is used as a fertilizer in agriculture, an electrolyte in batteries, a flux in soldering and metalworking, and a component in fire extinguishers and cleaning products.