In lanthanides,with increase in atomic number,atomic radius decreases,except for the element $\underline{ X }$. What is $\underline{ X }$?

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	$(v)$ $Gd$
-	$(vi)$ $Dy$

Which among the following lanthanoids has the smallest atomic size?

What is the cause of lanthanoid contraction?

Given below are two statements:
Statement $I$: $CeO_{2}$ can be used for the oxidation of aldehydes and ketones.
Statement $II$: Aqueous solution of $EuSO_{4}$ is a strong reducing agent.
In the light of the above statements,choose the correct answer from the options given below:

What is the correct order of ionic radii for the $+3$ oxidation state in $Ce, La, Pm,$ and $Yb$?