In the extraction of aluminium

Process X: employed for red bauxite to remove iron oxide (main impurity)

Process Y:(Serpeck's process): used for white bauxite to remove Z (main impurity) then,

Select correct option for the process X and impurity Z.

(X) Red bauxite contains the impurities of oxides of iron and silicates. In Baeyer process, alumina is dissolved by reacting sodium hydroxide solution leaving behind the insoluble oxide of iron. 

(Y) White bauxite contains the impurity of silica which is removed by Serpeck's method. 

$\begin{array}{l}{\mathrm{Al}}_2{\mathrm{O}}_3+{\mathrm{N}}_2+3\mathrm{C}\stackrel{{1800}^{\mathrm{o}}\mathrm{C}}{\to }2\mathrm{AlN}+3\mathrm{CO};\\ {\mathrm{SiO}}_2+2\mathrm{C}\stackrel{{1800}^{\mathrm{o}}\mathrm{C}}{\to }\mathrm{Si}+2\mathrm{CO}\\ \mathrm{AlN}+3{\mathrm{H}}_2\mathrm{O}\to \mathrm{Al}{\left(\mathrm{OH}\right)}_3+{\mathrm{NH}}_3;\\ 2\mathrm{Al}{\left(\mathrm{OH}\right)}_3\stackrel{\mathrm{\Delta }}{\to }{\mathrm{Al}}_2{\mathrm{O}}_3+3{\mathrm{H}}_2\mathrm{O}\end{array}$