Which of the following elements is not an actinoid?

The most basic hydroxide among the following is-

Which general symbol is used to represent lanthanoids?

Arrange the ions $Ce^{3+}$,$La^{3+}$,$Pm^{3+}$,and $Yb^{3+}$ in the increasing order of their ionic radii.

The $f$ orbitals are half-filled and completely filled,respectively,in which of the following lanthanide ions?
(Given: Atomic numbers: $Eu=63, Sm=62, Tm=69, Tb=65, Yb=70, Dy=66$)

Which of the following $f$-block elements exhibits the highest oxidation state?