Why among the lanthanides `Ce`,(III), can be easily oxidised to `Ce(IV)` (At. No. of Ce=58). Explain why?
Or of the lanthanides,cerium (At.Nos.58) forms a tetrapositive ion `Ce^(4+)` in aqueous solution. Why?

Answer

`Ce(II)` having the configuration `4f^(1)5d^(@)6s^(@)` can easily lose an electron to acquire the configuration `4f^(@)` and from Ce(IV). In fact , this is the only`(+IV)` lanthanide which exists in solution.