Provide two written definitions of an oxidation-reduction reaction and for each definition tell which reactant is reduced and which is oxidized. Then tell which of the two definitions is the most comprehensive.

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.