According to the question Why is charge = nALe n is the charge density (number of electrons per unit volume). Which of the electrons in a metal wire are involved in current flow? Only the unbounded to the nucleus (electron gas) I suppose. Or only some part of them? What is the amount for a cooper wire?
Current is conducted due to loosely held electrons present in a metallic lattice. (refer metallic bond on wiki). Note the electrons are loosely held to the neucleus and they are not free to fly away. When a potential difference is applied across a metallic conductor these electrons move from low potential to high potential giving rise to an electric current in the opposite direction (according to the convention). Note that, all the electrons in the conductor experience this at the same time, and hence a neglegible time is needed to light a light bulb (although the drift velocity of electrons is very low). Hope this will help.:)