Answer:
Explanation:
Oxidation:
1) Oxidation involve the removal of electrons.
2) Oxidation occur when oxidation state of atom of an element is increased.
Reduction:
1) Reduction involve the gain of electron.
2) Reduction is occur when number of electrons increased in an atom and oxidation state decreased.
Consider the following reactions.
4KI + 2CuCl₂  →  2CuI  + I₂  + 4KCl
the oxidation state of copper is changed from +2 to +1 so copper get reduced.
CO + H₂O  →  CO₂ + H₂
the oxidation state of carbon is +2 on reactant  side and on product side it becomes  +4 so carbon get oxidized.
Na₂CO₃ + H₃PO₄  →  Na₂HPO₄ + CO₂ + H₂O
The oxidation state of carbon on reactant side is +4. while on product side is  also +4 so it neither oxidized nor reduced.
H₂S + 2NaOH → Na₂S + 2H₂O
The oxidation sate of sulfur is -2 on reactant side and in product side it is also -2 so it neither oxidized nor reduced.
The  most comprehensive definition is 2nd definition which involves the increase or decrease in oxidation state.
