Periodic Classification of Elements — Science STD 10 — Question

Inert gases could be placed in Mendeleev’s Periodic Table without disturbing the original order.
Noble gases; like Helium, Neon and Argon had been mentioned by various scientists even before Mendeleev. But these gases could be grouped together as noble gases much later than Mendeleev’s discovery. Mendeleev used 63 elements till his periodic table because these were the only known elements till his time. However, he was bold enough to leave gaps in his periodic table. He had predicted that that more elements would be discovered in times to come.
Mendeleev’s Periodic Table was the first comprehensive attempt to classify elements on the basis of their chemical properties. This is the main reason that new elements could be easily placed in Mendeleev’s Periodic Table without disturbing the original order.