The correct answer is All of the above. Explanation & Key Takeaways: • Carbon has an electronic arrangement of 2,4. In diamond, each carbon shares electrons with four other carbon atoms - forming four single bonds. Diamond and Graphites are Allotropes of carbon. • Diamond has a very high melting point (almost 4000°C). Very strong carbon-carbon covalent bonds have to be broken throughout the structure before melting occurs. It is very hard. This is again due to the need to break very strong covalent bonds operating in 3-dimensions. • Diamond also doesn't conduct electricity. All the electrons are held tightly between the atoms and aren't free to move. Hence statement (a) is correct. • It is insoluble in water and organic solvents. • There are no possible attractions that could occur between solvent molecules and carbon atoms that could outweigh the attractions between the covalently bound carbon atoms. • The rigid structure, held together by strong covalent bonds, makes diamonds very hard. This physical property makes diamonds useful for cutting tools, such as diamond-tipped glass cutters and rock and oil rig drills. Hence statement (d) is correct • Graphite is insoluble in water and organic solvents - for the same reason that diamond is insoluble. Attractions between solvent molecules and carbon atoms will never be strong enough to overcome the strong covalent bonds in graphite. • Graphite has a giant covalent structure in which each carbon atom is joined to three other carbon atoms by covalent bonds the carbon atoms form layers with a hexagonal arrangement of atoms the layers have weak forces between them each carbon atom has one non-bonded outer electron, which becomes delocalized. This makes them appear as a 2-Dimensional Sheet-like structure. Hence statement (b) is correct • Figure: The structure of Graphite. • Graphite also conducts electricity. The delocalized electrons are free to move throughout the sheets. Hence statement (c) is correct