(i) When a copper object remains in damp air for a considerable time, then copper reacts slowly with carbon dioxide and water in air to form a green coating of basic copper carbonate on its surface. If corroded copper vessels are treated with lemon which is acidic in nature, the acid solution dissolves green coloured basic copper carbonate and makes them look shiny.
(ii) It is easier to obtain metals from their oxides (by reduction) than from sulphides. So before reduction, the metal sulphide ore is converted into metal oxide.
(iii) Copper metal is the next best conductor of electricity after silver metal. So electric wires are made up of copper (as silver being a costly metal can not be used for making electric wires).