Which one of the following is a radioactive lanthanide?

If the atomic number of an element is $58,$ it will be placed in the periodic table in the

Fill in the blanks:
$1.$ In the elements of the actinoid series,the last electron enters the ........... orbitals.
$2.$ Inner transition elements are the elements of the .......... series.
$3.$ If electrons are filled in the $5f$ series,those elements are called ....... elements.
$4.$ Many elements of the actinoid series are ......... .

Given below are two statements:
Statement $I$: $CeO_{2}$ can be used for the oxidation of aldehydes and ketones.
Statement $II$: Aqueous solution of $EuSO_{4}$ is a strong reducing agent.
In the light of the above statements,choose the correct answer from the options given below:

Observe the following $f$-block elements: $Eu (Z=63)$; $Pu (Z=94)$; $Cf (Z=98)$; $Sm (Z=62)$; $Gd (Z=64)$; $Cm (Z=96)$. How many of the above have half-filled $f$-orbitals in their ground state?

In the lanthanide series,the basicity of the lanthanide hydroxides: