Which group of elements could be placed in Mendeleev's Periodic Table without disturbing the origina

Which group of elements could be placed in Mendeleev's Periodic Table without disturbing the original order? Give reason.

Answer - Noble gases. According to the Mendeleev's classification, the properties of elements are the periodic function of their atomic masses and there is a periodic recurrence of elements with similar physical and chemical properties. Noble gases being inert, could be placed in a separate group without disturbing the original order.