Question

Electroplating is not provided to be used for:
A. shining appearance
B. protection of metal against corrosion
C. fine finishing to the surface
D. hardening the metals

Answer 1

Electroplating is a general name for processes that create a metal coating on a solid substrate through the reduction of cations of that metal by means of a direct electric current. The part to be coated acts as the cathode (negative electrode) of an electrolytic cell; the electrolyte is a solution of a salt of the metal to be coated; and the anode (positive electrode) is usually either a block of that metal, or of some inert conductive material. The current is provided by an external power supply.

Complete step by step answer:
Electroplating is widely used in industry and decorative arts to improve the surface qualities of objects such as resistance to abrasion and corrosion, lubricity, reflectivity, electrical conductivity, or appearance. It may also be used to build up thickness on undersized or worn-out parts, or to manufacture metal plates with complex shape, a process called electroforming. It is also used to purify metals such as copper.
Hardening is a metallurgical metalworking process used to increase the hardness of a metal. The hardness of a metal is directly proportional to the uniaxial yield stress at the location of the imposed strain. A harder metal will have a higher resistance to plastic deformation than a less hard metal. Thus, electroplating cannot be used for the hardening of metal.
The correct option is D. hardening the metals.

Note:
The term "electroplating" may also be used occasionally for processes that use an electric current to achieve oxidation of anions onto a solid substrate, as in the formation of silver chloride on silver wire to make silver/silver-chloride electrodes.. Electropolishing, a process that uses an electric current to remove metal cations from the surface of a metal object, may be thought of as the opposite of electroplating.