Chemical leaching is useful in the concentration of

Correct Option is: A. bauxite

Solution: 

• Chemical leaching is the type of process of a solute becoming detached or extracted from its carrier substance by the help of solvent. 
• In the concentration of Bauxite, Chemical leaching is used.
• Copper pyrites  is one of the sulphide ore, so a Froth floatation method is used.
• Method for separating cassiterite from gangue is Hydraulic Washing method is used.