What is the maximum oxidation state of $Th$?

Mischmetal is an alloy consisting mainly of

Which of the following is responsible for the lanthanoid contraction?

Write the electronic configurations of the elements with the atomic numbers $61$,$91$,$101$ and $109$.

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.

$A$ lanthanoid has $n$ unpaired electrons and another lanthanoid has $(14-n)$ unpaired electrons. It means: