Question

According to electrochemical theory of corrosion involves:
A. Cathodic dissolution of metal
B. Cathodic deposition of metal
C. Anodic dissolution of metal
D. Anodic deposition of metal

Answer 1

Hint- In order to deal with this question first we have to understand the electrochemical corrosion then we will proceed further by using its reaction to find the correct answer amongst the options by checking for the reaction going on in the phenomenon of corrosion.

Complete answer:
Electrochemical metal corrosion happens as electrons from atoms on the metal surface are passed to an suitable electron-acceptor or depolarizer. Water must be present to serve as a medium for the transport of ions.
Oxygen, acids and the cations of the less active metals are the most popular depolarizers.
In corrosion $F{e^{2 + }}$ gets oxidized to $F{e^{3 + }}$ which takes place on anode surface.
Reaction :
Anode: $Fe\left( s \right) \to F{e^{2 + }} + 2{e^ - }$
Cathode: ${O_2} + 4{H^ + } + 4{e^ - } \to 2{H_2}O$
Overall reaction:
$
  2Fe\left( s \right) + {O_2} + 4{H^ + } \to 2F{e^{2 + }} + 2{H_2}O \\
  4F{e^{2 + }} + {O_2} + \left( {2 + 4x} \right){H_2}O \to 2Fe{}_2{O_3}.x{H_2}O + 4{H^ + } \\
$
So, $F{e^{3 + }}$ gets deposited on the metal surface.
Hence, electrochemical theory of corrosion involves anodic deposition of metal.

So, option D is the correct option.

Additional information- Many of the ceramic materials are almost completely corrosion-proof. The tight chemical bonds that bind them together leave the system with very little free chemical energy; they can be seen as already corroded. It is almost always a simple dissolution of the material or chemical reaction, rather than an electrochemical process, when corrosion does happen. The lime applied to soda-lime glass to minimize its solubility in water is a typical example of corrosion safety in ceramics; while it is not quite as soluble as pure silicate salt, regular glass forms sub-microscopic defects when exposed to moisture.

Note- Corrosion is a natural process that converts a refined metal into a more chemically stable form such as oxide, hydroxide, or sulfide. Corrosion may be characterized as the chemical processes degrading the materials. Of such, by far the most important is electrochemical corrosion of metals, in which the oxidation cycle is accelerated by the presence of an effective electron acceptor, often referred to as a depolarizer in corrosion chemistry.