The high electrical conductivity of metals is primarily due to MOBILE ELECTRONS.
Metals generally have valence electrons which are not attached to any atom, these electrons are mobile and they move around freely within the structure of metals when electric current is applied to the metals. When electric current is applied to a particular metal, free electrons will move through the metal, passing the electrical charge around as they move. The passage of the electricity will be very high if the resistance to the flow of electricity is low.