Selenium is element 34, a non-metal of the p block, in group 16, period 4. Its ground-state configuration is [Ar] 3d10 4s2 4p4, and it usually shows the oxidation states -2, 0, 2, 4, 6.
It was discovered in 1817, by Berzelius.
Name origin: the Greek selene, 'moon'.
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