Which of the following oxidation states is common for all lanthanides?

Which one of the following statements concerning lanthanide elements is false?

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

Which of the following elements are included in the actinoid series?

For the general electronic configuration $(n-2)f^{1-14}(n-1)d^{0-1}ns^2$,if $n=7$,the configuration belongs to which series?

Consider the following statements:
$I$. $La(OH)_3$ is the least basic among hydroxides of lanthanides.
$II$. $Zr^{4+}$ and $Hf^{4+}$ possess almost the same ionic radii.
$III$. $Ce^{4+}$ can act as an oxidizing agent.
Which of the above is/are true?