What best explains why metals are good conductors of electricity?

Metals are good conductors of electricity primarily due to the behavior of their valence electrons. In metallic bonding, the valence electrons are not bound to individual atoms but are instead delocalized, meaning they can move freely throughout the metallic structure. This creates what is often referred to as an 'electron sea' surrounding a lattice of positively charged metal ions.

The freedom of movement of these delocalized electrons allows them to transfer kinetic energy and electric charge easily when a voltage is applied. This high mobility of charge carriers is what enables metals to conduct electricity efficiently.

In contrast, other concepts related to valence electrons, such as transferring them to form ions or sharing them in covalent bonds, do not account for the key characteristic of metallic bonding that allows for this conductivity. Thus, the unique arrangement and behavior of valence electrons in metals with delocalization is what fundamentally explains their excellent electrical conductivity.