Which element from the following is radioactive?

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

Determine whether the following statements are True $(T)$ or False $(F)$:
$(a)$ Actinoid contraction is greater than lanthanoid contraction.
$(b)$ Actinoids are elements of the $4f$ series.
$(c)$ All actinoid elements have a $7s^2$ configuration.

Which of the following elements shows the greatest similarity to the lanthanoids?

State the consequences of lanthanoid contraction. Explain the formation of coloured ions by lanthanoids.

When Lanthanoids $(Ln)$ react with oxygen $(O_2)$,what is the product $X$?