Why is graphite a good conductor of electricity but diamond is not?

Explanation

In a graphite molecule, each carbon atom has valence electrons in it. In a graphite crystal, each carbon atom is joined to only three other carbon atoms by covalent bonds.

Since only three valence electrons of each carbon atom in graphite are used in bond formation, the fourth valence electron of each carbon atom remains free, making graphite a good conductor of electricity.

In a diamond crystal, each carbon atom is linked. to four other carbon atoms by strong covalent bonds leaving no free electrons making a diamond crystal non-conductor of electricity.