Which one among the following statements about graphite is correct ?

Graphite and diamond are allotropes of carbon with different structures and properties. In graphite, each carbon atom is bonded to three others in a hexagonal planar layer (sp² hybridization). This leaves one valence electron per carbon atom free or "delocalized," which allows graphite to conduct electricity. In contrast, diamond has a rigid tetrahedral structure (sp³ hybridization) where all valence electrons are involved in single covalent bonds, making it an electrical insulator.

• Option A: Diamond is the hardest natural substance; graphite is soft and used as a lubricant.
• Option B: Both are pure allotropes of carbon (100% carbon).
• Option D: Diamond has a uniform C-C bond length (~1.54 Å), while graphite has shorter bonds within layers (~1.42 Å) and much larger distances between layers (~3.35 Å).