Question

What is the chemical formula of rust?
A. $ F{e_3}{O_4} $
B. $ F{e_2}{O_4} $
C. $ F{e_2}{O_3} $
D. $ F{e_3}{O_2} $

Answer 1

Hint :Rust is the general name for oxides of iron and hydroxides of iron. Formation of rust takes place when iron is exposed to oxygen and moisture for a long period of time. This process is called rusting of iron and where chemical reaction takes place between iron and oxygen.

Complete Step By Step Answer:
Rust is a general name of iron oxide. It is of reddish brown color. It is formed by the reaction of iron and oxygen with water or moisture of air.
Rust consist of hydrated $ Iron(III)oxides $ having formula $ F{e_2}{O_3}.n{H_2}O $ and $ Iron(III)oxide - hydroxide $ having formula as $ FeO(OH),Fe{(OH)_3} $ .
This process is called rusting of iron.
The rusting of iron is an electrochemical process that begins with the transfer of electrons from iron to oxygen. iron behaves as a reducing agent and releases the electrons while oxygen behaves as a reducing agent and gains the electrons.
In the rusting the key reaction is the reduction of oxygen:
 $ {O_2} + 4{e^ - } + 2{H_2}O \to 4O{H^ - } $
It forms hydroxide ions after that oxidation of iron take place as:
 $ Fe \to F{e^{2 + }} + 2{e^ - } $
The following redox reaction occurs in the presence of water and fasten the formation of rust:
 $ 4F{e^{2 + }} + {O_2} \to 4F{e^{3 + }} + 2{O^{2 - }} $
After that acid base reaction takes place and rust forms as:
 $ F{e^{2 + }} + 2{H_2}O \rightleftharpoons Fe{(OH)_2} + 2{H^ + } $
Now, dehydration takes place as:
 $ \begin{gathered}
  Fe{\left( {OH} \right)_2}\; \rightleftharpoons {\text{ }}FeO{\text{ }} + \;H2O \\
  Fe{\left( {OH} \right)_3}\; \rightleftharpoons {\text{ }}FeO\left( {OH} \right){\text{ }} + \;H2O \\
  2\;FeO\left( {OH} \right){\text{ }} \rightleftharpoons {\text{ }}F{e_2}{O_3}\; + \;H2O \\
\end{gathered} $
Hence, option C is correct.

Note :
Rust is permeable to air and water, so the interior metallic iron beneath a rust layer that continues to corrode. For the prevention of rust coating is required that preclude rust formation or can say avoid the water contact with iron.
Galvanization is a method of prevention of rust, in which an object is to be protected by a layer of metallic zinc by either hot-dip galvanizing or electroplating. Zinc is traditionally used because it is cheap, adheres well to steel, and provides cathodic protection to the steel surface in case of damage to the zinc layer.