Q.What is the origin of electrical conductivity of metals ?

There are two fundamentally different mechanisms by which an electric current can flow through matter. Metallic (electronic) conduction is the direct flow of free, delocalised valence electrons through a metal's conduction band under an applied potential; no ions move and no chemical change accompanies it, so metals and graphite are called electronic conductors. Electrolytic (ionic) conduction, by contrast, is the flow of current through a molten ionic compound or an aqueous solution of an electrolyte, carried by the physical migration of the electrolyte's own ions toward the oppositely-charged electrode; because material ions themselves are transported and discharged at the electrodes, electrolytic conduction is always accompanied by a chemical (redox) change. Substances that dissociate into mobile ions in the …