What is the electronic configuration of $Ce$ $(Z = 58)$?

Name a member of the lanthanoid series which is well known to exhibit $+4$ oxidation state.

Identify the correct statements from the following :
$I$. The ionic radius of $Pr^{3+}, Dy^{3+}$ and $Sm^{3+}$ follow the order,$Sm^{3+} > Pr^{3+} > Dy^{3+}$.
$II$. $Eu^{2+}$ acts as a strong reducing agent.
$III$. $Pu$ exhibits $+7$ oxidation state.

Write the atomic number,name,symbol,and electronic configuration of Actinium and the Actinoids.

Knowing that the chemistry of lanthanoids $(Ln)$ is dominated by its $+3$ oxidation state,which of the following statements is incorrect?

More number of oxidation states are exhibited by the actinoids than by the lanthanoids. The main reason for this is