Answer: B. Diamond is a giant covalent solid in which each carbon atom is covalently bonded to four others, arranged in a regular tetrahedral lattice. Statement B describes this correctly.
Option A is wrong: graphite is a lubricant because the layers are held to each other by weak intermolecular forces, not strong covalent bonds. The layers can slide.
Option C is wrong: graphite does conduct electricity (delocalised electrons between layers), but \(\text{SiO}_2\) does not — all valence electrons in \(\text{SiO}_2\) are locked into localised covalent bonds, so it is an insulator.
Option D is wrong: iodine changes from solid to gas on gentle warming because the intermolecular forces between \(\text{I}_2\) molecules are weak, not because the covalent bonds inside each \(\text{I}_2\) molecule are weak. The I–I bond itself is fairly strong; it's the dispersion forces between molecules that break.
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