The most important active step in the development of the periodic table was taken by

Which one of the following statements for $D.I.$ Mendeleev is incorrect?

What is the importance of the Periodic Table?

Why do we need to classify elements?

State whether the following statements are true or false:
$(i)$ The chart of elements presented by $Courtois$ could predict the stoichiometry of oxides of some metals.
$(ii)$ $Li, Na, Rb$ are known as $Döbereiner's$ triads.
$(iii)$ In $1863$,$Newlands$ classified the $56$ discovered elements into $18$ groups.
$(iv)$ $Mendeleev's$ periodic table is based on the atomic number of elements.

"The properties of the elements are periodic function of their atomic numbers." This statement was given by: