What characteristic makes metals good conductors?

Metals are known for their excellent conductivity primarily due to the presence of free electrons. In metallic structures, atoms are arranged in a lattice where electrons can move relatively freely. These free electrons are not bound to any particular atom, which allows them to carry electric charge efficiently throughout the metal when an electric field is applied. This movement of electrons facilitates the conduction of both electric current and thermal energy.

The other options present characteristics that do not contribute to conductivity in metals. High resistance, for instance, suggests that a material impedes the flow of electric current, which is the opposite of good conductivity. A low boiling point is generally characteristic of nonmetals rather than metals and does not relate to electrical conductivity. While the absence of impurities can contribute to better conductivity by reducing resistance, it is not the fundamental characteristic that defines why metals are good conductors in the first place. Thus, the defining factor remains the presence of free electrons, enabling efficient conduction in metallic materials.