Solution

(a) Platinum, gold and silver are used to make jewellery because these are low reactive metals. So they rarely corrode and hence do not lose their shine and lustre.

(b) The reaction of these substances with oxygen is highly exothermic which may cause fire, also they react with water to form base so they are kept in oil.

(c) This is because aluminium is good conductor of heat and electricity. To prevent its reaction with food at high temperature a protective layer of aluminium oxide ($$Al_2O_3$$ ) is formed which prevent further corrosion.

(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction because it is easier to obtain metal from its oxide as compared with its sulphides or carbonates ore.