Limiting compositions of $f$-block hydrides are

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?

Determine whether the following statements are True $(T)$ or False $(F)$:
$(a)$ All actinoid elements have a $7s^1$ configuration.
$(b)$ All actinoid elements have a $7s^0$ configuration.
$(c)$ There are no electrons in the $7s$ orbital of actinoids.

Which of the following elements exhibits oxidation states other than $+3$?

Which series of elements are radioactive?

Which of the following properties of lanthanoids is $NOT$ true?