The process of 'leaching' is typically employed for the concentration of ores that are:
Correct: C
Leaching is a chemical concentration method where the powdered ore is treated with a suitable chemical reagent that selectively dissolves the desired metal compound, leaving the impurities behind. This method is used for ores like bauxite (aluminium ore) where it's treated with concentrated NaOH solution, or for gold and silver ores using cyanide solutions. It relies on the chemical reactivity of the ore with a specific solvent.