(i) Digestion of food in stomach : During digestion, the complex food is broken into simpler form. Therefore, it is a type of decomposition reaction.
(ii) Combustion of coal in air : During combustion the coal burns in air to form CO2,H2O along with the evolution of heat. Thus, it is a type of exothermic decomposition reaction.
(iii) Heating of limestone : When limestone is heated strongly, it breaks into CO2 and lime. Thus, it is a type of thermal decomposition reaction.