The substance which conducts current in the solid state is –

The structure of graphite is unlike most other network substances. It is formed in 'sheets' of carbon atoms, each of which is bonded to only three others. The fourth valence electron of the carbon atom is delocalized and can move between the different layers, therefore carrying an electrical charge through the network of carbon atoms, a conductor is a material which contains movable electric charges. Unlike diamond (another carbon allotrope), graphite is an electrical conductor, a. semimetal.