(A) : Alumina is leached from bauxite using caustic soda.

(R) : Leaching is used when ore alone, but not gangue is soluble in a suitable solvent.

The separation of alumina from the impurities in the ore bauxite is usually accomplished by the Bayer Process. In this process, the ground bauxite is leached with caustic soda $\left(\mathrm{NaOH}\right)$ to produce soluble sodium aluminate $\left({\mathrm{NaAlO}}_2\right)$, leaving the impurities in the insoluble residue.

Ores mined from the earth are usually contaminated with a large number of impurities such as soil, sand, etc known as gangue. Leaching is used when ore is soluble in a suitable solvent but not gangue.

Therefore, Option A is the correct answer.