Leaching is a process of:
A. Reduction
B. Concentration
C. Refining
D. Oxidation
E. None of these

Hint: We study the term leaching in metallurgy. Metallurgy is a process that is used for the extraction of metals in their pure form from their ore. Now you should try to answer this question.

Complete step by step answer:
We should know that leaching is a process widely used in extractive metallurgy. Here the ore is treated with chemicals to convert the valuable metals within into soluble salts while impurity remains insoluble.
These can then be washed out and processed to give the pure metal.
Leaching is easier to perform because it requires less energy and it is much less harmful as no gaseous pollution occurs.
Drawbacks of leaching include lower efficiency and the often significant quantities of waste effluent, which are usually either highly acidic or alkali as well as toxic, for example, bauxite tailings.

Therefore, we can conclude that the correct answer to this question is option C.

Additional information:
We should know that leaching is done in long pressure vessels which are cylindrical or of horizontal tube form, we call them autoclaves.
The autoclave leach process can also be found in the metallurgy of zinc. This can be best described by the following chemical reaction:
$2ZnS+O_{ 2 }+2H_{ 2 }SO_{ 4 }\quad \rightarrow \quad 2ZnSO_{ 4 }+2H_{ 2 }O+2S$

Note: We should know that there are four types of leaching depending on the type of ore -
1. Cyanide leaching (for gold ore)
2. Ammonia leaching (for crushed ore)
3. Alkali leaching (for bauxite ore)
4. Acid leaching (for sulfide ore)