In which of the following properties do $Lanthanoids$ and $Actinoids$ show similarity?

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

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.

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

Which of the following elements exhibits a $+4$ oxidation state?

Lanthanoid ions with $4f^7$ configuration are :
$A$. $Eu^{2+}$
$B$. $Gd^{3+}$
$C$. $Eu^{3+}$
$D$. $Tb^{3+}$
$E$. $Sm^{2+}$
Choose the correct answer from the options given below :