SeO3, or selenium trioxide, is a chemical compound composed of one selenium atom and three oxygen atoms. It is a colorless, oily liquid that is highly reactive and can act as a strong oxidizing agent. Selenium trioxide is primarily used in the production of other selenium compounds and in various chemical reactions. In addition to its industrial applications, SeO3 is also important in the field of chemistry for synthesizing organoselenium compounds. Due to its reactivity, it must be handled with care, as it can be hazardous to health and the environment. Proper safety measures are essential when working with this compound.