Sulfurous acid (H2SO3) is a weak diprotic acid formed by the dissolution of sulfur dioxide (SO2) in water, existing primarily in equilibrium as hydrated SO2 rather than a discrete molecular species. It is unstable in pure form and decomposes readily, releasing SO2 gas. Commonly encountered as an aqueous solution, it serves as a reducing agent, antioxidant, and preservative in food processing, winemaking, and paper manufacturing. The acid partially dissociates into bisulfite (HSO3-) and sulfite (SO3^2-) ions, contributing to its antimicrobial properties. Due to its reactivity with oxygen, it is often handled under inert conditions. In analytical chemistry, it is used for titrations and as a bleaching agent for delicate materials.