(i) As we know pure water is not a good conductor of electricity. But by the addition of a small amount of acid during electrolysis of water, water could be decomposed to hydrogen gas and oxgyen gas easily.
(ii) On dissolving ammonium chloride (NH4Cl) in water in a test tube, the test tube becomes cold as it takes heat from the surrounding water. Hence, it is an endothermic reaction.
(iii) Paint is applied on iron articles to prevent them from rusting (corrosion).