Answer: B. Graphite consists of layers of carbon atoms covalently bonded in hexagonal rings. The layers are held together only by weak intermolecular forces, allowing them to slide over one another easily — this is why graphite acts as a lubricant.
A is wrong: diamond's hardness comes from each carbon being bonded to four other carbons (tetrahedrally), not three.
C is wrong: in silicon dioxide, each silicon is surrounded by four oxygen atoms (not oxide ions — \(\text{SiO}_2\) is covalent, not ionic).
D is wrong: iodine is a simple molecular solid (\(\text{I}_2\) molecules held by weak intermolecular forces). Its melting point is low, not high — the bonds within molecules are strong, but breaking them isn't what melting does.
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