Caustic soda, also known as sodium hydroxide or lye, is an inorganic compound with the formula NaOH. It is highly soluble in water and absorbs moisture and carbon dioxide from the air. This compound is widely used in industrial and household cleaning products, pH adjustment in manufacturing processes, and industries like pulp and paper, textiles, drinking water treatment, and soap production. Sodium hydroxide is available in both solid (flakes, prills, briquettes) and liquid forms at various concentrations.