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 configurations of these elements.

Answer

`+4=._(58)Ce.,_59Pr,._60Nd,._65Tb,._66Dy`
`+2=._60Nd,._62Sm,._63Eu,._69Tm,._70Yb`
`+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^(1),4f^(2))`or close to `4f^(7)(e.g.,4f^(7) or `4f^(6))`