CBSE Class 10 Answered
Oxygen and sulphur are nonmetals, and selenium, tellurium, and polonium are metalloid semiconductors that means, their electrical properties are between those of a metal and an insulator. Nevertheless, tellurium, as well as selenium, is often referred to as a metal when in elemental form.
Metal chalcogenides are common as minerals. For example, pyrite FeS2 is an iron ore. The rare mineral calaverite is the ditelluride AuTe2.
The formal oxidation number of the most common chalcogen compounds is −2. Other values, such as −1 in pyrite, can be attained. The highest formal oxidation number +6 is found in sulfates, selenates and tellurates, such as in sulfuric acid or sodium selenate Na2SeO4.