In the extraction of aluminium Process X : employed for red bauxite to remove iron oxide (mainly impurity Process Y : (Serpeck's process) : used for white bauxite to remove Y (mainly impurity) then, Select correct option for the process X and impurity Z.

Bayer applied red bauxite to remove iron oxide. While Serpeck's process: applied for white bauxite to remove $Si{O}_2\mathit{-}$. Using Serpeck's method, white bauxite is beneficially processed. It includes purging impurities. $Si{O}_2+2C\to Si+2CO$ 

Hence the correct option is B.