alleryInert pair effect causes stability of:
ATl(III)
BTl(I) over Tl(III) (s² pair retained)
CAlways higher oxidation
DSame oxidation
Answer & Solution
Correct answer: B. Tl(I) over Tl(III) (s² pair retained)
**Inert pair effect:** heavier 6th-period elements (Tl, Pb, Bi) prefer lower oxidation state with their s² pair untouched.
Tl(I), Pb(II), Bi(III) are more stable than Tl(III), Pb(IV), Bi(V).
Relativistic effects contribute.
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