Answer: The sum of its first three ionisation enthalpies is very high.
- A Its atomic size is very large
- B The sum of its first three ionisation enthalpies is very high
- C It has a very low electronegativity and a large atomic radius
- D It has filled d-orbitals
Correct answer: B. The sum of its first three ionisation enthalpies is very high
Explanation: Removing three electrons from small boron needs a very large amount of energy, so forming B<sup>3+</sup> is not favoured; boron bonds covalently instead.
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.