Why do heavy p-block elements like Thallium (+1) and Lead (+2) favor oxidation states 2 units lower than their group valency? (Hard)
Answer and explanation
Correct answer: D. Inert pair effect
- Step 1: Relativistic contraction and poor shielding by intervening 4f and 5d electrons pull the valence 6s electrons closer to the nucleus. Step 2. The 6s^2 pair becomes chemically unreactive ('inert'), favoring lower oxidation states by 2 units (Tl+ over Tl3+, Pb2+ over Pb4+). Answer: Inert pair effect (reluctance of valence s-electrons to participate in bonding). Why not the others: Lanthanide contraction causes shrinkage not expansion; heavy p-block metals have lower electronegativity; hybridization is altered by 6s inertness.
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