Which among the following lanthanoids forms the most stable $+2$ oxidation state?

If $Ln$ represents a lanthanoid element,find the general formula of lanthanoid hydroxide.

Which lanthanoid element exhibits $+2$ and $+3$ oxidation states?

For the general electronic configuration $(n-2)f^{1-14}(n-1)d^{0-1}ns^2$,if $n=7$,the configuration belongs to which series?

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:

The element californium belongs to the family of