Photoelectric Uses of Selenium and Tellurium

Selenium and tellurium are both photosensitive semiconductors that is, their electrical conductivity is markedly greater when exposed to light. In the language of band theory, electromagnetic radiation can promote electrons from valence bands to conduction 

Sulfuric acid has such a variety of applications it is difficult to gain a good appreciation of its pervasive role in the chemical industry. More than half of it is used to produce superphosphate and other fertilizers (see pp. 484—485). Other major uses include the manufacture of hydrochloric acid from salt, represented in Equations (17.27) and (17.28), 

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