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

Explanation

Noble gases could be placed in Mendeleev.s periodic table without disturbing the original order.
Noble gases are inert due to completely filled valence electron shell. They are present in extremely low concentrations in our atmosphere and usually do not form any chemical compound with other elements. During the development of the periodic table by Mendeleev, these gases were not known. After their discovery, they were placed in a new group separately since their properties did not resemble that of any other group in the periodic table. So, their presence did not affect the existing order of Mendeléey.s periodic table.