Lanthanides and actinides resemble in

Which element from the following lanthanoids has a half-filled $f$-orbital in its observed and expected electronic configuration?

Explain the size of actinoid elements and their ions.

Explain $f$-block elements of the periodic table in detail.

Fill in the blanks:
$1.$ The size of $M^{3+}$ ions in the actinoid series ........... with an increase in atomic number.
$2.$ The common oxidation state of elements in the actinoid series is .......... .
$3.$ The appearance of elements in the actinoid series is like .......... .

Name the members of the lanthanoid series which exhibit $+4$ oxidation state and those which exhibit $+2$ oxidation state. Try to correlate this type of behavior with the electronic configurations of these elements.