What is the electronic configuration of $Nd^{2+}$?

The lanthanide contraction is responsible for the fact that

The element californium belongs to the family of

The $f$ orbitals are half-filled and completely filled,respectively,in which of the following lanthanide ions?
(Given: Atomic numbers: $Eu=63, Sm=62, Tm=69, Tb=65, Yb=70, Dy=66$)

Identify the formula of compound $(B)$ formed in the following reaction:
$(i)$ Lanthanoids $(Ln)$ are burnt in oxygen to form compound $(A)$.
$(ii)$ Compound $(A)$ reacts with $CO_2$ in excess to form compound $(B)$.

The point of dissimilarity between lanthanides and actinides is