Which series of elements are radioactive?

The reason for the greater range of oxidation states in actinoids is attributed to:

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

Which elements exhibit nearly identical properties?

Compare the chemistry of actinoids with that of the lanthanoids with special reference to:
$(i)$ electronic configuration
$(ii)$ atomic and ionic sizes
$(iii)$ oxidation state
$(iv)$ chemical reactivity.

The chemistry of the actinoid elements is not so smooth as that of the lanthanoids. Justify this statement by giving some examples from the oxidation states of these elements.