Which of the following is not an actinide?

Match the properties given in List-$I$ with the elements given in List-$II$:

List-$I$ (Property)	List-$II$ (Element)
$(A)$ Lanthanoid showing $+4$ oxidation state	$(i)$ $Pm$
$(B)$ Lanthanoid showing $+2$ oxidation state	$(ii)$ $Ce$
$(C)$ Radioactive lanthanoid	$(iii)$ $Lu$
$(D)$ Lanthanoid with $4f^7$ configuration in $+3$ state	$(iv)$ $Eu$
$(E)$ Lanthanoid with $4f^{14}$ configuration in $+3$ state	$(v)$ $Gd$
-	$(vi)$ $Dy$

Although $(+3)$ oxidation state is the characteristic oxidation state of lanthanoids,cerium shows $(+4)$ oxidation state also. Why?

The total number of rare-earth elements is

$A$ reduction in atomic size with an increase in atomic number is a characteristic of elements of

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.