Name the member of the lanthanoids series which exhibit+4 oxidation states and those which exhibit+2 oxidation state. Try to correlate this types of behavior with the electronic configuration of these elements.

Explanation

`+4` oxidation sate: `""_(58)Ce,""_(59)Pr,""_(65)Tb`.
+2 oxidation state : `""_(60)Nd,""_(62)Sm,""_(63)Tm,""_70Yb`.
In general +2 oxidation state is exbibited by the elements with configuration `5d^(0)6s^(2)` so that two electrons may be easily lost. Similarly +4 oxidation sate is shown by the elements which after losing four electrons acqure configuration either close of `4f^(0)` or `4f^(7)`.