Name the members of the lanthanoid series which exhibit + 4 oxidation states and those which exhibit +2 oxidation states. Try to correlate this type of behaviour with the electronic configuration of these elements.

Explanation

`+ 4` oxidation state exists in `""_(58)Ce, ""_(59)Pr, ""_(60) Nd_(65) Tb` and `""_(66)Dy`.
+ 2 oxidation state exists in `""_(60)Nd, ""_(62)Sm, ""_(63)Eu, ""_(69)Tm` and `""_(70)Yb.`
Generally, + 2 oxidation state is exhibited by the elements with configuration `5d^(0)6s^(2)` so that two electrons may be easily lost. Similarly, + 4 oxidation state is shown by the element which after losing four electrons acquire configuration either close to `4f^(0)` or `4f^(7)`