Step-by-step explanation:
For a substance to be able to conduct electricity it is necessary to have free electrons.
Since, metals are the substances that have more number of electrons as compared to non-metals. Hence, metals are good conductors of electricity.
For example, copper, nickel, aluminium are all good conductors of heat and electricity.
Thus, we can conclude that mobile or free electrons is the property of metals which makes them good conductors of electricity.