Question

Taking stability as the factor, which one of the following represents correct relationship?

• A. Inl₃ > Inl
• B. AlCl > AlCl₃
• C. TII > TII₃
• D. Tll₃ > TlCl

Answer 1

The Correct Option is C

In assessing the stability of compounds, we often consider the oxidation state and the concept of inert pair effect, especially in heavier elements of groups 13 and 15 of the periodic table. 

The inert pair effect refers to the phenomenon where the s-electrons of the valence shell remain non-ionized or unshared in compounds of post-transition metals. This effect is more pronounced as you move down a group in the periodic table.

In the case of thallium, a group 13 element, the +1 oxidation state is more stable than the +3 oxidation state due to the inert pair effect. Here, thallium prefers to retain its 6s² electrons, leading it to exist commonly in the Tl⁺ state.

Comparing thallium compounds: TII (where thallium is in +1 oxidation state) is more stable than TII₃ (where thallium is in +3 oxidation state). Thus, the correct relationship reflecting stability is: TII > TII₃.

Answer 2

The stability of a compound is often related to the charge on the central atom and the nature of its bonding with the ligands. In this case, TII (Tl⁺¹) refers to thallium(I) ions, and TII₃ (Tl³⁺) refers to thallium(III) ions.
Generally, lower oxidation states (e.g., Tl⁺) are more stable than higher oxidation states (e.g., Tl³⁺) for heavy elements like thallium. This is due to the presence of additional electron shells that can provide increased shielding and stability for lower oxidation states.
Option (C) TII > TII₃ reflects this principle and correctly represents the relationship based on stability.
Therefore, the correct option is (C) : TII > TII₃