Give reaction for the following :
(a) In `(III)` is more stable than in `(I)` in aqueous solution.
(b) `InCl_(3)` undergoes disproportionation but `InCl` does not.
( c) Unlike `In^(oplus), Tl^(oplus)` is more stable with respect to disproportionation.
(d) `Ga^(oplus)` undergoes disproportionation reaction.

Explanation

(a) Due to inert pair effect, indium shows `+1` and `+3` oxidation states, But since this effect is less prominent in indium, `+3` oxidation state is more stable than `+1` oxidation state. Consequently, in aqueous solution, less stable `In^(oplus)` undergoes disproportionation (auto-oxidation-reduction) to form stable `In^(3+)` and In.
`3I_((aq))^(oplus) overset("Disproportionation") rarr In_((aq))^(3+) + 2In_((s))`
(b) Both `In` and `Tl` show `+1` and `+3` oxidation states in their compound due to inert pair effect. But in `In`, the higher oxidation state, i.e. `+3` is more stable than the lower oxidation state, i.e. `+1`. Therefore, `InCl` undergoes disproportionation in aqueous solution.
`3InCl_((aq)) overset("Disproportionation")rarr 2In_((s)) + InCl_(3(aq))`
However, in `Tl, + 3` oxidation state is less stable than `+1` oxidation state , hence, `TlCl` does not undergo disproportionation reaction.
( c) Due to inert pair. both `In` and `Tl` can exhibit `+1` and `+3` oxidation states. But inert pair effet is more prominent in `Tl` than `In`. As a result result, `+1` oxidation state is more stable in `Tl` as compared to In, and `+3` oxidation state is more stable in In as compared to `Tl`. Hence, `In^(oplus)` easily indergoes disproportionation, whereas `Tl^(oplus)` is stable with respect to disproportionation.

(d) Due to the inert pair effect, gallium exhinits both `+1` and `+3` oxidation states. But since `+3` oxidation state is more stable than `+1` oxidation state, `Ga^(oplus)` undergoes disproportionation to form `Ga` metal and `Ga^(3+)` ion in aqueous solution.
`3Ga_((aq))^(oplus) rarr Ga_((aq))^(3+) + Ga_((s))`.