(i) CO2 is not a pollutant when present in the atmosphere upto a certain per cent. Rather, it helps to maintain the temperature of the earth. Combustion of coke is harmful as it increases the concentration of CO2 in the atmosphere causes global warming (greenhouse effect).
(ii) Decomposition of limestone (CaCO3) gives quicklime (CaO) which combines with water to form slaked lime, Ca(OH)2 which after putting on the walls, combines with CO2 of the air to form CaCO3.
(iii) Tiffin boxes made up of steel are either tin plated or nickel plated to protect them from rusting. However, tin-plating is preferred because tin is non-poisonous and hence, does not contaminate the food kept in them.
Chromium plating is done on bicycle handles and car bumpers made up of iron to protect them from rusting and give them a shining appearance.
(iv) A photographic film used in black and white photography is a celluloid film coated with silver chloride. Its working is based on the decomposition of silver chloride in the presence of sunlight.