The correct answer is (4) highly mobile electrons in the valence shell
The explanation:
-A metal consists of a lattice of atoms, each with a shell of electrons. This is also known as a positive ionic lattice.
- The outer electrons are free to dissociate from their parent atoms and travel through the lattice, creating a sea of electrons, his valence electrons are what freely move around making the metal a conductor.
-When an electrical potential difference is applied across the metal, the electrons drift from one end of the conductor to the other under the influence of the electric field.