Which lanthanoid from the following exhibits $f^{14}$ configuration in the $+3$ oxidation state?

The number of elements from the following that do not belong to lanthanoids is:
$Eu, Cm, Er, Tb, Yb$ and $Lu$

Which of the following statements are correct?
$I$. $P$ has the least negative electron gain enthalpy among $P, S, Cl$, and $F$.
$II$. In $Eu$ and $Yb$, lanthanoid contraction is not observed.
$III$. $Ce(OH)_3$ is the most basic among lanthanoid hydroxides.
$IV$. The radii of $Na$ and $Na^+$ are $95 \ pm$ and $186 \ pm$ respectively.

In lanthanides,with an increase in atomic number,the atomic radius decreases,except for the element $\underline{X}$. What is $\underline{X}$?

What are the elements of the $f$-block called?

Which of the following lanthanoid elements exhibits common oxidation states of $+2$ and $+3$?