(i) The food taken by the living beings is ultimately broken down to glucose by the digestive system. The glucose so formed is slowly oxidised to carbon dioxide and water with the release of heat energy. Thus, respiration is an exothermic process.
(ii) On heating lead nitrate crystals, nitrogen dioxide gas is evolved, which is reddish brown in colour.
(iii) Antioxidants are added to fat and oil containing foods to prevent rancidity.