Selenium dioxide

Selenium dioxide, also known as selenious oxide, selenous oxide, or selenium(IV) oxide, is a chemical compound. Its chemical formula is SeO2. It contains selenium in its +4 oxidation state. It also contains oxide ions. It is toxic.
Properties.
Selenium dioxide is a white solid. It dissolves in water to make selenous acid. It easily evaporates. The vapor smells like horseradish sauce. It can burn the nose. It reacts with bases to make selenites.
Preparation.
Selenium dioxide can be made by burning selenium in air. It can also be made by reacting selenium with nitric acid or hydrogen peroxide. Another way to make it is to heat selenous acid.
Occurrence.
Selenium dioxide is very rare as a mineral. It only is in places where coal caught on fire and the selenides were oxidized to selenium dioxide.
Uses.
Selenium dioxide is used in making organic compounds. Selenium dioxide is used as a coloring in glass. Cobalt in glass makes a blue color. When a little selenium dioxide is added, the glass becomes colorless. When more selenium dioxide is added, the glass becomes ruby red.
Safety.
Selenium dioxide can dissolve in water to make toxic selenium compounds. Swallowing any more than a very tiny amount can cause selenium poisoning. Selenium dioxide is a weak oxidizing agent and does not catch things on fire.