Name the hardest natural substance known.

8 Name the black substance of pencil. Will the current flow through the electrical circuit when we use the sharpened ends of the pencil to complete the circuit? 9 How does graphite act as a lubricant? 11 Which of the following molecules is called buckministerfullerene?

C₉₀ C₆₀ C₇₀ C₁₂₀

12 Give the name and structural formulae of an alkyl group.