The separation of $Lanthanoid$ elements is based on which of the following?

Which of the following elements are analogous to the lanthanides?

Provide the electronic configurations of lanthanoids $(4f)$ series elements $(Ln)$ and their ions $Ln^{2+}$ and $Ln^{3+}$,and state their characteristics.

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

The electronic configurations of bivalent europium and trivalent cerium are
(atomic number : $Xe=54, Ce=58, Eu=63$ )

Identify the correct statements about lanthanoids:
$I$. $Ce^{4+}$ and $Tb^{4+}$ act as oxidising agents.
$II$. $Eu^{2+}$ and $Yb^{2+}$ act as reducing agents.
$III$. Mischmetal is an alloy of $95 \%$ lanthanoid metal and $5 \%$ iron.
$IV$. $La^{3+}$ and $Ce^{4+}$ are diamagnetic in nature.