(a) Copper is a good conductor of electricity. It is ductile and less expensive; therefore, it is used for making electrical wires.
(b) Graphite is a non-corrosive non-metal and a poor conductor of electricity. It is also cheap and insoluble in water, acids and bases. It is inert (does not react) to the electrolytes present in the dry cells. Thus, it makes a good material for an electrode.