Answer:
The correct answer is C. The carbon atoms are arranged differently in diamond than in graphite.
Step-by-step explanation:
Diamond and graphite are solid and different structures despite being formed by carbon atoms.
In the case of graphite, the C atoms exhibit sp² hybridization. This means that each carbon atom is linked to another 3 by a covalent bond, forming laminar structures (that is, sheets of carbon atoms are formed.).
In the diamond, the C atoms exhibit a sp³ hybridization, each one joining 4 other C atoms through a covalent bond and forming a three-dimensional structure.
This difference in structures explains that graphite is one of the softest materials, because the links between the sheets are very weak and it is easily exfoliable while diamond is the hardest substance known due to precisely that three-dimensional structure of covalent bonds.
Finally, the correct answer is C. The carbon atoms are arranged differently in diamond than in graphite.