Three pairs of compounds are given below, identify that compound in each of the pairs which has group 13 element in more stable oxidation state. Give reason for your choice.
(i) `TlCl_(3).TlCl` (ii) `AlCl_(3).AlCl` (iii) `InCl_(3).InCl`

Explanation

(a) TlCl more stable than `TlCl_(3)` due to inert pair effect. `TlCl_(3)` is less stable and covalent in nature but TlCl is more stable and ionic is nature
(b) Due to absence of d-orbitals, Al does not show inert pair effect. Hence, its most stable oxidation state is +3. Thus, `AlCl_(3)` is much more stable then AlCl. Further, in the solid or the vapour state `AlCl_(3)` covalent in nature but in aqueous solutions, it ionises to form A `Al^(3+)(aq) and Cl^(-)(aq)` ions
(c) Due to inert pair effect, indium exists in both +1 and +3 oxidation states out of which +3 oxidation state is more stable is more stable than +1 oxidation state. In other words, `InCl_(3)` is more stable than InCl. Being unstable, In Cl undergoes disproportionation reaction
`3InCl(aq)rarr2ln(s)+ln^(3+)(aq)+3Cl^(-)(aq)`.