Among $Ce(4f^{1} 5d^{1} 6s^{2})$,$Nd(4f^{3} 6s^{2})$,$Eu(4f^{7} 6s^{2})$ and $Dy(4f^{10} 6s^{2})$,the elements having highest and lowest $3^{rd}$ ionisation energies,respectively are

Consider the following two statements:
$Statement-I:$ Among $Mg, Al, Mg^{2+}, Al^{3+}$,the one having the smallest size is $Al^{3+}$.
$Statement-II:$ $Eu$ has an exceptionally high atomic radius among lanthanide elements.
The correct answer is:

Arrange the following metal complexes/compounds in the increasing order of spin-only magnetic moment. Presume all three are high-spin systems.
(Atomic numbers: $Ce = 58$,$Gd = 64$,and $Eu = 63$.)
$(a)$ $(NH_4)_2[Ce(NO_3)_6]$
$(b)$ $Gd(NO_3)_3$
$(c)$ $Eu(NO_3)_3$
Answer is:

Which element in the lanthanoids is radioactive?

$(i) La(OH)_3$ 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?

The lanthanoid that would show color is