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

$(a)\;\text{Tin and lead} \\(b)\;\text{Chromium.} \\(c)\; \text{ Manganese} \\ (d)\;\text{Zinc}$

The gemstone ruby is an impure form of alumina having impurity Chromium
The colouration of stone is because of its impurity.
Hence b is the correct answer.
edited Apr 1