In option (b), (ii) and (iv) are disproportionation reaction are.
A disproportionation reaction is a redox reaction in which a compound of intermediate oxidation state converts to two different compounds, one of higher and one of lower oxidation states.
In this reaction, oxidation number of
Cl increases from
0( in
Cl2) to
+1 (in
ClO−)and decreases 0 (in
Cl2 ) to
−1 (in
Cl−). Therefore,
Cl2 is both oxidised to
ClO−and reduced to
Cl−. Since,
Cl−ion cannot act as an oxidising agent (because it cannot decrease its oxidation number lower than
−1 ).
Therefore,
Cl2 bleaches substances due to oxidising action of hypochlorite,
ClO−ion. (IV) Disproportionation of
H2O2
One molecule of hydrogen peroxide is oxidised to oxygen and the second molecule of hydrogen peroxide is reduced to water.