Selenium Acid, also known as selenous acid, is a chemical compound with the formula H₂SeO₃. It is a colorless, odorless liquid that is soluble in water and is primarily used in various industrial applications, including the production of selenium compounds and as a reagent in chemical synthesis. This acid is derived from selenium dioxide when it reacts with water. It is important in the field of chemistry due to its properties as a reducing agent and its role in the study of selenium chemistry. However, it can be toxic and should be handled with care.