Answer: The +1 state becomes more stable down the group, Tl+ being quite stable.
- A The +1 state becomes more stable down the group, Tl+ being quite stable
- B The +3 state becomes progressively more stable moving down the group
- C Boron commonly shows the +1 state
- D Aluminium is most stable in the +1 state
Correct answer: A. The +1 state becomes more stable down the group, Tl+ being quite stable
Explanation: Due to the inert pair effect the ns2 electrons become reluctant to bond down the group, so the +1 state grows in stability and Tl+ is more stable than Tl3+.
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.