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Selenium is a non-metallic chemical element, member of the group XVI of the periodic table. In chemical activity and physical properties it resembles sulphur and tellurium. Selenium appears in a number of allotropic forms: the most popular are a red amorphous powder, a red crystalline material, and a grey crystalline metal like form called metallic selenium. This last form conducts electricity better in the light than in the dark and is used in photocells. Selenium burns in air and is unaffected by water, but dissolves in concentrated nitric acid and alkalis.
Selenium has good photovoltaic and photoconductive properties, and it is used extensively in electronics, such as photocells, light meters and solar cells. The second largest use of selenium is in the glass industry: selenium is used to remove colour from glass, to give a red colour to glasses and enamels. The third min use, taking about 15% is sodium selenite for animal feeds and food supplements. Selenium can also find applications in photocopying, in the toning of photographs. Its artistic use is to intensify and extend the tonal range of black and white photographic images. Other uses of selenium are in metal alloys such as the lead plates used in storage batteries and in rectifiers to convert AC current in DC current. Selenium is used to improve the abrasion resistance in vulcanized rubbers. Some selenium compounds are added to anti-dandruff shampoos