How were the positions of isotopes of varoius elements decided in the Modern periodic table?

Observe the following elements in the modern periodic table?

What is the basis of modern periodic table?

The following tables shows the position of six elements A, B, C, D, E ,and F in the periodic table? Using the table answer the following question: Write a common name for the elements C and F.

The following tables shows the position of six elements A, B, C, D, E and F in the periodic table? Using the table answer the following question: which element is non- metal with valency of 3?

The following tables shows the position of six elements A, B, C, D, E and F in the periodic table? Using the table answer the following question:Which element will form only covalent compounds?

The following tables shows the position of six elements A, B, C, D, E and F in the periodic table? Using the above table answer the following question: which element is a metal with valency 2 ?

The following tables shows the position of six elements A, B, C, D, E ,and F in the periodic table? Using the table answer the following question:Out of D and E, which one has a bigger atmic radius and why?

Name the elements discovered after mendeleev's periodic table?

Two elements X and Y have atomic numbers 12 and 16 respectively. Write the electronic configuration for these elements. To which period of the modern perioidic table to these two elements belong? What type of bond will be formed between them and why?