Answer: Both assertion and reason are true and the reason explains the assertion.
- A The assertion is false but the reason is true
- B Both statements are true but the reason does not correctly explain the assertion
- C The assertion is true but the reason is false
- D Both assertion and reason are true and the reason explains the assertion
Correct answer: D. Both assertion and reason are true and the reason explains the assertion
Explanation: Monomeric AlCl<sub>3</sub> has only a sextet on Al; by dimerising through chloride bridges each Al attains an octet, so dimer formation is driven by octet completion.
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.