Graphite, which is an allotrope of carbon, is a conductor of electricity. But diamond, another allotrope of carbon is not a conductor of electricity. Why?

Explanation

In diamond each carbon atom is linked to another four carbon by covalent bond surrounding it. So there is no free electron present to conduct the electricity. In graphite each carbon is linked to another three carbon atoms covalently forming a sheet like structure. The presence of free electron which are not involved in the covalent bonding makes graphite a good conductor of electricity.