Question

The $+1$ oxidation state of thallium is more stable than its $+3$ oxidation state because of

• A. its atomic size
• B. its ionization potential
• C. inert pair effect
• D. diagonal relationship

Answer 1

Answer: (C)

Inert pair effect due to this thallium is found commonly in $+1$ oxidation state.
It has electronic configuration as
$[Xe]4f^{14}5d^{10}6s^{2}6p^1$
and shows oxidation states $+3$ and $+1$.