(a). Explain why `Mn^(3+)` is less stable than `Mn^(22+)` and `M^(4+)` ions?
(b). Standard reduction potential of copper is greatr than that of hydrogen yet is librates hydrogen from a concentrated solution of hydrochloric acid. Explain this fact with proper reasoning.
`Cu^(2+)+2etoCu_(s)`
`E_((Cu^(2+))/(Cu))^(ɵ)=0.34"volt"`
`2H^(o+)+2etoH_(2(g))`
`E_((H^(o+))/(H_2))=0.00"volt"`
(c). An aqueous solution of `FeCl_3` is slightly yellowish in colour.
(d). `Cu(I)` compounds are not known in aqueous solution.

Explanation

(a). `Mnto3d^5,4s^2`, `Mn^(3+)to3d^4,4s^(0)`
`Mn^(2+)to3d^5,4s^0`,`Mn^(4+)to3d^3,4s^0`
On the basis of electron configuration `Mn^(2+)` and `Mn^(4+)` are expected to be more stable, hence `Mn^(3+)` undregoes disproportionation.
`2Mn^(3+)toMn^(2+)+(mn^(4+)`
(b). When copper is treated with conc.HCl then formation of stable complex ion `[CuCl_4]^(2-)` along with liberation of `H_2` gas takes place.
`Cu+4HCl_((conc.))to[CuCl_4]^(2-)+2H^(o+)+H_2uarr]`
(c). An equeous solution of `FeCl_3` is colloidal. It is yellowish in colour due to Tyndall Effect.
(d). `Cu(I)` compounds undergo disproportionation in aqueous medium.
`Cu_2Cl_2toCuCl_2+Cu`