is a class of organic compounds that contain a sulfonic acid functional group, which consists of a sulfur atom bonded to three oxygen atoms (one of which is double-bonded) and a hydrogen atom. Sulfonic acids are strong acids and are widely used in various industrial processes and chemical reactions.

Some common uses of sulfonic acid include:
1- Surfactants: Sulfonic acids are used as surfactants in the production of detergents, soaps, and cleaning agents. They help to lower the surface tension of liquids, allowing them to spread more easily and improve their cleaning properties.
2- Dyes and Pigments: Sulfonic acids are used in the production of dyes and pigments. They can enhance the solubility, stability, and color properties of these compounds.
3- Catalysts: Sulfonic acids are employed as catalysts in various chemical reactions, including esterification, hydration, and polymerization processes.