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

Explanation

`+4` oxidation state is given by : `""_(58)Ce,""_(59)Pr, ""_(60)Nd, ""_(65)Tb, ""_(66)Dy`
`+2` oxidation state is given by : `""_(60)Nd,""_(62)Sm,""_(63)Eu,""_(69)Tm,""_(70)Yb`
+2 oxidation state is exhibited when the lanthanoid has the configuration `5d^(0)6s^(2)` so that 2 electrons are easily lost. +4 oxidation state is exhibited when the configuration left is close to `4f^(0)("e.g., "4f^(0),4f^(1),4f^(2))` or close to `4f^(1)("e.g., "4f^(7)" or "4f^(8))`.