Copper becomes green when exposed to moist air for a long period . This is due to :

Question

(a) The formation of a layer of cupric oxide on the surface of copper.\[\](b) The formation of a layer of basic carbonate of copper on the surface of copper .\[\](c) The formation of a layer cupric hydroxide on the surface of copper.\[\] (d) The formation of basic copper sulphate layer on the surface of the metal.