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# The gemstone Saphire is an impure form of alumina having impurity of

$(a)\;\text{Nickel} \\(b)\;\text{Cobalt.} \\(c)\;\text{Manganese} \\ (d)\;\text{Tin}$

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A)
Sapphire is the impure form of alumina which contains cobalt (Co) as impurity.
Hence b is the correct answer.