State the Modern Periodic Law.

Atomic numbers of a few elements are given below: $10, 20, 7, 14$.
$(a)$ What would be the electronic configuration for each of these elements?
$(b)$ Determine the valency of these elements.

Up to which element was the Law of Octaves found to be applicable?

The three elements $A$,$B$,and $C$ with similar properties have atomic masses $X$,$Y$,and $Z$ respectively. The mass of $Y$ is approximately equal to the average mass of $X$ and $Z$. What is such an arrangement of elements called? Give one example of such a set of elements.

Write the formulae of chlorides of Eka-silicon and Eka-aluminium,the elements predicted by Mendeleev.

Which of the following statements about the Modern Periodic Table is correct?