Which one of the following lanthanoids does not form $MO_{2}$? [$M$ is lanthanoid metal]

Given below are two statements:
Statement $I$: In the Lanthanoids,the formation of $Ce^{+4}$ is favoured by its noble gas configuration.
Statement $II$: $Ce^{+4}$ is a strong oxidant reverting to the common $+3$ state.
In the light of the above statements,choose the most appropriate answer from the options given below:

Identify the isoelectronic pair of ions from the following.

If the ionic radius of $_{57}La^{3+}$ is $1.06 \ \mathring{A}$,then the ionic radius of $_{71}Lu^{3+}$ will be approximately close to which of the following values in $\mathring{A}$?

Which one of the following elements shows the maximum number of different oxidation states in its compounds?

Select the incorrect statement about lanthanides.