NaH3O2 is the chemical formula for sodium metabisulfite. It is a white or colorless crystalline powder that is soluble in water. It is used as a food preservative and as a reducing agent in photography and other industries.

Sodium metabisulfite is a type of sulfite, which means that it contains the sulfite ion (SO32-). Sulfites are reducing agents, which means that they can donate electrons to other molecules. This property makes them useful as food preservatives, as they can prevent the oxidation of food and keep it from spoiling.

Sodium metabisulfite is also used as a reducing agent in photography and other industries. In photography, it is used to develop film and to fix prints. In other industries, it is used to reduce the color of dyes and to bleach paper.