(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 $\mathrm{CO}_2,\ \mathrm{H}_2\mathrm{O}$ 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 $\mathrm{CO}_2$ and lime. Thus, it is a type of thermal decomposition reaction.