Assertion : Diamond is a bad conductor. Reason : Graphite is a good conductor.

In diamond, each carbon atom is in $s p^3$ hybridised state and linked to four other carbon atoms tetraherallyby covalent bonds. Since there is no mobile electron present, diamond is a bad conductor of heat and electricity. In graphite each carbon atom is in $s p^2$ hybridised state and is linked to three other carbon atoms in a hexagonal planar structure. The $\pi$-electrons are free to move throughout the entire layers, therefore graphite is a good conductor of heat and electricity.