Identify the lanthanoid element from the following.

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.

More number of oxidation states are exhibited by the actinoids than by the lanthanoids. The main reason for this is

What is the basic character of lanthanoid hydroxides?

Explain the size of actinoid elements and their ions.

The percentage $(\%)$ of iron in pyrophoric mischmetal is ...........