Question

Which group of elements could be placed in Mendeleev's periodic table later on, without disturbing the order? Give reason.

Answer 1

Noble gases are the group of elements which could be placed in Mendeleev's periodic table later on, without disturbing the order. This is  because they are inert (unreactive) elements, as their valence shells are completely filled with electrons. Therefore, Mendeleev decided to include these elements in a separate group.