Identify the correct decreasing order of atomic radii from the following.

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.

Which of the following pairs show $+2$ oxidation state?

$A$ member of the Lanthanoid series which is well known to exhibit $+4$ oxidation state is

Which series of elements are radioactive?

Which lanthanoid from the following has the highest first ionisation enthalpy $(IE_1)$?