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

(i) Due to strong inert pair effect , +1 oxidation state of Tl is more stable than `+3`. Since compounds in lower oxidation state are ionic but covalent in higher oxidation state, therefore `TlCl_(3)` is less stable and covalent in nature but `TlCl` is more stable and is ionic in nature.
(ii) Due to absence ofd-orbitals, Al does not show inert pair effect, Therefore its most stable oxidation state is +3. Thus, `AlCl_(3)` is much more stable than `AlCl`. Further in the solid or the vapour state, `AlCl_(3)` is covalent in nature but in aqueous solution , it ionizes to form `Al^(3+) (aq)` and `Cl^(-) (aq)` ions.
(iii) Due to inert pair effect, indium exists in both +1 and +3 oxidation states out of which +3 oxidation state is more stable than +1 oxidation state.In other words,`InCl_(3)` is more stable than `InCl`. Being unstable, ICl undergoes disproportionation reaction.
`3ICl (aq) rarr 2 In (s) + In^(3+) (aq) +3Cl^(-) (aq)` ,