Decomposition Reaction: It is a very simple type of chemical reaction in which a single compound splits into two or more simple substances under suitable condition. It is just opposite of combination reaction.
Thermal decomposition: When a decomposition reaction is carried out by heating it is called thermal decomposition reaction.
CaCO3 (s) -----heat----> CaO(s) + CO2(g)
Electrolytic decomposition: When a decomposition reaction is carried out with the help of electric current it is called electrolytic decomposition reaction. This process is also called electrolysis.
2H2O(l) -----electric current---> 2H2(g) + O2(g)
