Answer: high ionisation energy.
- A large atomic size
- B high ionisation energy
- C low electronegativity
- D metallic character
Correct answer: B. high ionisation energy
Explanation: The very high total ionisation energy needed to remove three electrons makes ionic B³⁺ compounds unfavourable.
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.