Assertion(A) : Bauxite is purified by leaching process.
Reason (R) : Aluminium oxide reacts with NaOH to form soluble sodium meta aluminate
 

Bauxite $\left({\text{Al}}_{\text{2}}{\text{O}}_{\text{3}}{\text{.2H}}_{\text{2}}\text{O}\right)$  is purified by leaching process. In this process bauxite is treated with NaOH  to form sodium meta aluminate. 
 ${\text{Al}}_2{O}_3.2H_{2}O+2NaOH\underset{200-{250}^{0}C}{\overset{45\%NaOH}{\to }}2NaAl{O}_2+3H_{2}O$