Most common oxidation states of $Ce$ $(cerium)$ are

Name the members of the lanthanoid series which exhibit $+4$ oxidation state and those which exhibit $+2$ oxidation state. Try to correlate this type of behavior with the electronic configurations of these elements.

In the context of the lanthanoids,which of the following statements is not correct?

Which statement is incorrect with reference to inner transition elements?

Which one of the following lanthanide ions does not exhibit paramagnetism?

What is the effect of lanthanoid contraction in the lanthanoid series of elements?