(a) Write one equation each for decomposition reaction when energy is supplied in the form of :
(i) heat , (ii) light.
(b) Account for the following :
(i) Paint is applied on iron articles.
(ii) Oil and fat containing food items are flushed with nitrogen .
(iii) When an iron nail kept in copper sulphate solution, blue colour of the solution fades and iron nail becomes brownish .

Explanation

(a) (i) `CaCO_(3)(S) overset Delta rarrCaO(S)+CO_(2)(g)`
(ii) `2AgBr overset("Sunlight")rarr2Ag+Br_(2)`
(b) (i) To protect the iron articles from corrosion . When iron articles are exposed to moist air , corrosion takes place . When the surface is covered by paint, it is not exposed to moist air .
(ii) To flush out any air or oxygen present in the packet . In the absence of oxygen , food items will not get rancid.
(iii) Since iron is more reactive than copper , it displaces copper from copper sulphate solution and the blue colour of solution fades . Due to the deposition of copper on iron nail , iron nail becomes brownish.