Let's evaluate each statement: (a) Diamond is a non- conductor of electricity: Correct. Diamond has a tetrahedral structure where each carbon atom is sp³ hybridized, and all valence electrons are involved in strong covalent bonds. There are no free electrons to conduct electricity. (b) Graphite has a two- dimensional sheet-like structure: Correct. Graphite consists of layers of carbon atoms arranged in hexagonal lattices. (c) Graphite conducts electricity: Correct. In graphite, each carbon atom is sp² hybridized, forming sigma bonds with three other carbon atoms. The remaining valence electron is delocalized in a pi system across the layers, allowing for electrical conductivity along the layers. (d) Diamond is used for rock drilling: Correct. Diamond is the hardest naturally occurring substance and is used in tools for cutting, grinding, and drilling, including rock drilling.