Answer: Carbon.
- A Carbon
- B Silicon
- C Germanium
- D Tin
Correct answer: A. Carbon
Explanation: Both diamond (sp³) and graphite (sp²) are allotropic forms of carbon; fullerene (C₆₀) is a third.
Diamond's rigid 3D tetrahedral network makes it the hardest natural material, while graphite's flat hexagonal sheets are held together only by weak forces, letting them slide past each other (used as a lubricant and in pencils).
Concept context
Covers the Boron family (Group 13: B, Al) and the Carbon family (Group 14: C, Si, Ge, Sn, Pb). Key topics include Lewis acid behaviour of BF₃, borax bead test, silicates, silicones, allotropes of carbon, and trends in properties down the group.