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EEJ MAIN Chemistry QUESTION #7156
Question 1
Thallium ($Tl$) can exist in both $+1$ and $+3$ oxidation states, whereas Aluminium ($Al$) is typically found only in the $+3$ state. What is the reason for this difference?
  • Inert pair effect✔️
  • Diagonal relationship
  • Lattice effect
  • Lanthanoid contraction
Correct Answer Explanation
As we move down Group 13, the $ns^2$ electrons become increasingly reluctant to participate in bonding due to poor shielding by $d$ and $f$ electrons. This is known as the Inert Pair Effect. For Thallium, the $+1$ oxidation state is more stable than $+3$, while for lighter elements like Al, the effect is negligible.