Question

Why is graphite good conductor of electricity but not diamond?

Answer 1

This is because the composition of graphite is layered where as the composition of diamond is as web.And graphite have a free electon in b/w layers while diamond have no free electron.

Answer 2

In a graphite molecule, one valence electron of each carbon atom remains free , Therefore graphite gained a name of a good conductor of electricity. Whereas in diamond, they have no free mobile electron.