Answer: Has accessible vacant 3d-orbitals.
- A Is more electronegative than carbon
- B Forms only ionic compounds
- C Has a smaller atomic size than carbon
- D Has accessible vacant 3d-orbitals
Correct answer: D. Has accessible vacant 3d-orbitals
Explanation: Silicon has empty 3d-orbitals that can accept additional electron pairs, allowing a covalency of six; carbon has no d-orbitals in its valence shell and is limited to four.
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.