Which of the following elements belongs to the actinoid series?

The most common lanthanide is

What are the elements of the $f$-block called?

On the basis of Lanthanoid contraction,explain the following :
$(i)$ Nature of bonding in $La_2O_3$ and $Lu_2O_3$.
$(ii)$ Trends in the stability of oxo salts of lanthanoids from $La$ to $Lu$.
$(iii)$ Stability of the complexes of lanthanoids.
$(iv)$ Radii of $4d$ and $5d$-block elements.
$(v)$ Trends in acidic character of lanthanoid oxides.

Which of the following elements exhibits oxidation states other than $+3$?

Which one of the following lanthanides exhibits $+2$ oxidation state with diamagnetic nature? (Given $Z$ for $Nd=60, Yb=70, La=57, Ce=58$)