$A$ reduction in atomic size with an increase in atomic number is a characteristic of elements of

Which of the following exhibits only $+3$ oxidation state?

The electronic configuration of Einsteinium is : (Given atomic number of Einsteinium $= 99$)

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.

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 $(B)$.

Which of the following properties is common to both lanthanoids and actinoids?