Oxidation-Reduction Reactions
(1) Oxidation: Oxidation is a process which involves; addition of oxygen, removal of hydrogen, addition of non-metal, removal of metal, Increase in +ve valency, loss of electrons and increase in oxidation number.
(i) Addition of oxygen: 2Mg + O2 
2MgO
(ii) Removal of hydrogen: H2S+Cl22HCl + S
(iii) Addition of Non-metal: Fe + S FeS
(iv) Removal of metal: 2KI+H2O22KOH+I2
(v) Increase in +ve valency : 
(vi) Loss of electrons (also known as de-electronation)
–e– –e– –e– –e– –e– –e– –e– –e–
Loss of electrons
(a) 
(Formation of proton)
(b) 
(De-electronation of 
)
(c) 
(De-electronation of iron)
(vii)Increase in oxidation number
(a) 
(From 0 to +2)
(b) 
(From +2 to +3)
(c) 
(From –1 to 0)
(2) Reduction: Reduction is just reverse of oxidation. Reduction is a process which involves; removal of oxygen, addition of hydrogen, removal of non-metal, addition of metal, decrease in +ve valency, gain of electrons and decrease in oxidation number.
(i) Removal of oxygen: 
(ii) Addition of hydrogen: 
(iii) Removal of non-metal
(iv) Addition of metal: 
(v) Decrease in +ve valency
(a) 
(+ve valency decreases)
(b) 
(–ve valency increases)
(vi) Gain of electrons (also known as electronation)
+e– +e– +e– +e– +e– +e– +e– +e–
Gain of electrons
(a) 
(Electronation of 
)
(b) 
(Electronation of 
)
(c) 
(Electronation of 
)
(vii) Decrease in oxidation number
(a) 
(From +2 to 0)
(b) 
(From +3 to +2)
(c) 
(From 0 to –1)