Why was group 0 missing in mendeveleve's?

Answer 1

Group 0, which corresponds to the noble gases, was initially missing in Mendeleev's Periodic Table because these elements were not discovered until later. Mendeleev's table was based on the properties and atomic weights of known elements at the time, primarily focusing on those that were reactive. The noble gases, being largely inert and rarely interacting with other elements, were not recognized until the late 19th century, leading to their absence in Mendeleev's original arrangement.