Hydrogen selenide

Hydrogen selenide, also known as hydroselenic acid, selenium hydride, or selane, is a chemical compound. Its chemical formula is H2Se. It is an acid. It contains hydrogen and selenide ions.
Properties.
Hydrogen selenide is a colorless gas that dissolves in water to make an acidic solution. It smells like rotten horseradish. It is very toxic. It burns easily, making selenium dioxide. It is similar to hydrogen sulfide, a gas that smells like rotten eggs. It is a strong reducing agent.
Preparation.
Hydrogen selenide can be made by hydrolysis of aluminium selenide. This reaction also makes aluminium hydroxide. It can be made by reacting hydrogen with powdered selenium at a high temperature. 
Uses.
It can be used to add selenide ion to organic compounds. It can also be used to make selenium by reacting it with sulfur dioxide. This makes selenium, sulfur, and water.