Amongst the given elements,which one exhibits a $+4$ oxidation state in an aqueous medium?

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.

The atomic number of cerium $(Ce)$ is $58$. The correct electronic configuration of $Ce^{3+}$ ion is

All those elements belong to $f-$block whose atomic numbers are

Which element from the following has a half-filled $4f$ orbital in its observed ground state?

The elements with atomic numbers $101$ and $104$ belong to,respectively