1.

Anhydrous alumina `(Al_(2)O_(3))` is known asA. emeraldB. corundumC. sapphireD. ruby

Answer» Correct Answer - B
It is natural aluminium oxide. It is a crystalline substance nearly as hard as diamond, used as an abrasive. Ruby is a red form of corundum, `Al_(2)O_(3)`, that owes its color to traces of `Cr`. Sapphire is a natural crystalline form of blue, transparent corundum, the color being due to traces of cobalt or other metals.


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