Answer:
Diamond has a giant molecular structure. Each carbon atom is covalently bonded to four other carbon atoms. A lot of energy is needed to separate the atoms in diamond. This is because covalent bonds are strong, and diamond contains very many covalent bonds.
Graphite on the other hand has flat layers of carbon atoms held by weak van der Waal's forces which makes Graphite a weak object and easily breakable.
As graphite contains layers of carbon atoms. The layers slide over each other easily because there are only weak forces between them, making graphite slippery. These electrons can move through the graphite, carrying charge from place to place and allowing graphite to conduct electricity.One valence electron of each carbon atom remains free, Thus making graphite a good conductor of electricity. Whereas in diamond, they have no free mobile electron. Hence there won't be flow of electrons That is the reason behind diamond are bad conductor electricity.These electrons are free to move between the layers in graphite, so graphite can conduct electricity.The forces between the layers in graphite are weak. This means that the layers can slide over each other.