There are three types of decomposition reaction they are:
1) Thermal decomposition : When a decomposition reaction is carried out by heating, it is called thermal decomposition reaction.
Example : CaCO3----> CaO + CO2
2) Photochemical decomposition : If the energy of sunlight is used to carry out the decomposition reaction, it is called photochemical decomposition.
Example: 2H2O2----> 2H2O + O2
3) Electrolytic decomposition : If the electric current is used to carry out decomposition reaction. It is called electrolytic decomposition.
Example : 2H2O ----> 2H2 + O2