The amounts of different substances liberated by the same quantity of electricity passing through the electrolytic solution are proportional to their chemicalequivalent weights.

Charge on one electron is 1.6 x 10^-19  C. 
1 mole of electron 6.023 x  10²³  electrons.
So charge on one mole of  electron = 1.6 x 10^-19  C  x  6.023 x  10²³  = 96500 C mol^-1

Primary batteries cannot be recharged and reused.

Secondary cell can be recharged and reused.

• A  fuel cell  is an  electrochemical cell  that converts the  chemical energy  of a fuel (often  hydrogen) and an  oxidizing agent  (often oxygen) directly into electrical energy  through a pair of  redox  reactions. 
• Fuel cells are different from most  batteries  in requiring a continuous source of fuel and oxygen (usually from air) to sustain the chemical reaction, whereas in a battery the chemical energy usually comes from metals and their ions or oxides  that are commonly already present in the battery, except in  flow batteries.
• Fuel cells can produce electricity continuously for as long as fuel and oxygen are supplied.

Setup of a Fuel cell:

In Corrosion, a metal  is oxidized by loss of electrons and results in the formation of oxides.

• Corrosion  is a  natural process  that converts a refined metal into a more chemically stable form such as  oxide, hydroxide, or  sulfide.
• It is the gradual destruction of materials (usually a  metal) by chemical and/or electrochemical reaction with their environment. 
• Corrosion engineering  is the field dedicated to controlling and preventing corrosion.

The best way to prevent corrosion is to prevent the surface of the metallic objects to come in contact with the atmosphere.

• The rusting of iron can be prevented by painting, oiling, greasing or varnishing its surface.
• Galvanization is another method of protecting iron from rusting by coating iron with a thin layer of zinc.
• Corrosion of iron is prevented by coating iron with non-xcorrosive substance like carbon. This process is termed as alloying .

Galvanization is a process in which iron is coated with reactive metal like Zn which get corroded hence preventing iron from corrosion.

Electro-Galvanization:

 A more reactive metal displaces a less reactive metal from the salt solution (refer to reactivity series).

The order  in which metals  displace each other from the solution of their salts can be given with the help of their standard electrode potential . Since magnesium has the least standard electrode potential so it is the most strong reducing agent.

So  the required order we get is:  Mg >Al >Zn >Fe >Cu

Reactivity Series:

The standard emf of a galvanic cell involving  3  moles of electrons in its redox reaction is  0.59V.

E º_cell ​= 0.59V
n=3
The equilibrium constant for the reaction of the cell is given by the expression: ln K = RT nFE º_cell ​
ln K = 8.314  ×298 ×3 ×96500 ×0.59 = 68.9
K ≈10³⁰

The equilibrium constant for the reaction of the cell is  10³⁰ .