Why are metales good electrical conductor?

Answer 1

the electron "gas" of unbound conduction band electrons present in all metals

Answer 2

Their electrons move freely. This is due to the bonding. In metallic bonding the nuclei are surrounded by a sea of electrons rather than discreet paired electrons with covalent bonds.
Metals are good conductors of both electric charges and heat because their electrons are "loose."

(info from physics book) Some good metal electrical conductors are copper which has a high conductivity, the best pure metal conductor is silver, aluminum is another good conductor. Some good metal electrical conductors are copper which has a high conductivity, the best pure metal conductor is silver, aluminum is another good conductor.