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. 

Stability in the aqueous medium depends on the hydration energy of ions when they attract to water to water molecules. In aqueous solution, Cu⁺ ion undergoes oxidises and reduces simultaneously

in aqueous to give Cu and Cu²⁺ ion.

 
The relative stability of different oxidation states can be seen from their 

 Electrode potentials  
Due to more reduction electrode potential value of Cu+, it undergoes oxidation reaction quite feasible. Hence, the copper (I) ion is not known in aqueous solution. 

(ii) The actinoids show a larger number of oxidation states because of the very small energy gap between the 5f, 6d and 7s subshells. The energies are decided on the basis of the (n+1) rule.

The (n+1) values of the three orbitals are under:

5f=5+3=8

6d=5+2=8

7s=7+ 1=8

All of the value comes to be same. Hence they have the same energy.