H2Se, or hydrogen selenide, is a chemical compound composed of two hydrogen atoms and one selenium atom. It is a colorless gas with a strong, unpleasant odor similar to that of rotten eggs. H2Se is highly toxic and can be harmful if inhaled or ingested, making safety precautions essential when handling it. In nature, hydrogen selenide can be found in volcanic gases and as a byproduct of certain industrial processes. It is used in various applications, including the production of selenium and in the synthesis of other chemical compounds. Due to its toxicity, H2Se is regulated in many countries.