The origin of the name Selenium comes from the Greek word 'Selênê,' meaning moon. Selenium was discovered and first isolated by Jöns Jakob Berzelius and Johann Gottlieb Gahn in 1817. One of the most common uses for selenium is in glass production the red tint that it lends to glass neutralizes green or yellow tints from impurities in the glass materials. Selenium is a non-metal with several allotropes: a black, vitreous form with an irregular crystal structure three red-colored forms with monoclinic crystal structures and a gray form with a hexagonal crystal structure, the most stable and dense form of the element. The selenium atom has a radius of 120 pm and a Van der Waals radius of 190 pm. The number of electrons in each of Selenium's shells is 2, 8, 18, 6 and its electron configuration is 3d 10 4s 2 4p 4. Selenium (atomic symbol: Se, atomic number: 34) is a Block P, Group 16, Period 4 element with an atomic radius of 78.96. Iridium's name is derived from the Greek goddess Iris, personification of the rainbow, on account of the striking and diverse colors of its salts. Iridium is found as an uncombined element and in iridium- osmium alloys. It will not react with any acid and can only be attacked by certain molten salts, such as molten sodium chloride. It is the most corrosion resistant metal known and is the second-densest element (after osmium). Iridium is a member of the platinum group of metals. In its elemental form, Iridium has a silvery white appearance. Iridium was discovered and first isolated by Smithson Tennant in 1803.

The iridium atom has a radius of 136 pm and a Van der Waals radius of 202 pm. It is unaffected by air, water, and acids, but dissolves in molten. The number of electrons in each of iridium's shells is and its electron configuration is 4f 14 5d 7 6s 2. Description: Iridium is a hard, lustrous, silvery metal of the so-called platinum group. Iridium (atomic symbol: Ir, atomic number: 77) is a Block D, Group 9, Period 6 element with an atomic weight of 192.217.

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Is iridium a metal or nonmetal