Assign reasons for the following :
(i) Copper (I) ion is not known in aqueous solution.
(ii) Actinoids exhibit greater range of oxidation states than lanthanoids.

Answer

(i) `Cu^(+)` ions are not stable in aqueous solution. `Cu^(+)` in aqueous solution undergoes disproportionation i.e.,
`2Cu^(+)(aq) to Cu^(2+)(aq)+Cu(S).`
(ii) lanthanoids are predominant species. Occasionally `+2` and `+4` ion in solution or in solid compounds are also obtained. This irregularity arised mainly from extra stability of empty, half filled f shell. There are a greater range of oxidation states which is in part attributed to the fact that the `5f,6d` and `7s` level are of comparable energies.