Which of the following lanthanoids exhibits a $+4$ oxidation state with an $f^7$ configuration?

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.

Which actinoid from the following has the smallest ionic size in the $+3$ oxidation state?

Arrange the ions $Ce^{+3}, La^{+3}, Pm^{+3},$ and $Yb^{+3}$ in the increasing order of their ionic radii.

In the lanthanide series,the basicity of the lanthanide hydroxides:

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