H2SeO3, known as selenous acid, is a chemical compound composed of selenium, oxygen, and hydrogen. It is a weak acid that can be formed by dissolving selenium dioxide in water. Selenous acid is often used in various chemical reactions and can act as a reducing agent. In its pure form, H2SeO3 appears as a colorless liquid. It is important in the field of chemistry, particularly in the study of selenium compounds. Selenous acid can also be involved in the synthesis of other selenium compounds and is relevant in analytical chemistry for detecting selenium in different samples.