All those elements belong to $f-$block whose atomic numbers are

Which of the following elements is not an actinoid?

The correct order of ionic radii of $Ce, La, Pm$ and $Yb$ in $+3$ oxidation state is:

Although $+3$ oxidation state is most common in lanthanoids,cerium still shows $+4$ oxidation state because:

Determine the correct $(T)$ and incorrect $(F)$ statements from the following:
$(a)$ The symbol for Lanthanum is $La$.
$(b)$ The name of the element $Lu$ is Lanthanum.
$(c)$ The electronic configuration of $La^{3+}$ and $Ce^{4+}$ contains $4f^0$.

In $+2$ oxidation state,which of the following lanthanoids act as reducing agents?