The 'shanks system' of leaching (i.e., counter-current multiple contact leaching) is used for

ANS:C - both (a) and (b).

The 'Shanks system' of leaching, also known as counter-current multiple contact leaching, is commonly used for the recovery of tannins from tree barks and woods, among other applications. This method involves the extraction of soluble components from solid materials by repeatedly contacting the solid with a solvent while continuously moving the solid and solvent in opposite directions (counter-current flow). This allows for efficient extraction of the soluble components from the solid material. While leaching sodium nitrate from Chilean nitrate-bearing rock may also involve similar principles of leaching, it is not specifically associated with the 'Shanks system' of leaching. Therefore, the correct answer is recovery of tannins from tree barks and woods.