Which actinoid elements have a $5f^{14}$ electronic configuration in their atoms?

Lanthanoid ions with $4f^7$ configuration are :
$A$. $Eu^{2+}$
$B$. $Gd^{3+}$
$C$. $Eu^{3+}$
$D$. $Tb^{3+}$
$E$. $Sm^{2+}$
Choose the correct answer from the options given below :

$(i) La(OH)_3$ is the least basic among lanthanide hydroxides. $(ii) Zr^{4+}$ and $Hf^{4+}$ have almost identical ionic radii. $(iii) Ce^{4+}$ can act as an oxidizing agent. Which of the above statements are correct?

Fill in the blanks:
$1.$ The atomic radii of the elements of the third transition series are .......... to those of the corresponding elements of the second transition series.
$2.$ Samarium melts at .......... $K$.
$3.$ The color of lanthanoid ions is due to the presence of .......... electrons.

Fill in the blanks given below:
$(i)$ Neptunium and Plutonium are obtained from ............ .
$(ii)$ Lanthanoid series and Actinoid series are known as ............ .
$(iii)$ The main energy level of an atom is called ............ .
$(iv)$ Elements that possess both metallic and non-metallic properties are called ............ .

Which one of the following elements shows the maximum number of different oxidation states in its compounds?