Selenium trioxide

Selenium trioxide, also known as selenium(VI) oxide and selenic oxide, is a chemical compound. Its chemical formula is SeO3. It contains selenium in its +6 oxidation state. It also contains oxide ions.
Properties.
Selenium trioxide is a white solid. It evaporates easily. It dissolves easily in water. It is not stable and breaks down to make selenium dioxide and oxygen when it is heated. It is a powerful oxidizing agent like all selenates. It dissolves in water to make selenic acid.
Preparation.
It can be made by reacting potassium selenate with sulfur dioxide. It can also be made by dehydrating (removing the water from) selenic acid with a strong dessicant, like phosphorus(V) oxide.