Why are isotopes of an element having different atomic masses placed at the same position in the periodic Table?

Two elements X and Y have atomic numbers 10 and 14 respectively. Identify the group numbers of these elements in the periodic table.

List any two properties of the elements belonging to the first group of the Modern Periodic Table.

Write two elements for each of the following: i. Alkali metals, ii. Noble gases.

Account for the following:

a. Cations are smaller in size than the corresponding atom.

b. The noble gases were discovered very late.