How would you account for the following :
(i) Among lanthanoids,Ln(III) compounds are predominant. However,occasionally in solution or in solid compound,`+2` and `+4` ions are also obtained.
(ii) The `E_(M^(2)//M)^(@)` for copper is positive `(0.34 V)` copper is the only metal in the first series of transition elements showing this behaviour.
(iii) The metallic radii of the third `(5d)` series of transition metals are nearly the same as those of the corresponding member of the second series.