On the basis of which important property did Mendeleev classify the elements in his periodic table? Was he able to stick to it firmly? Explain.

The telluric helix was given by

What is the importance of the Periodic Table?

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 a periodic function of their atomic numbers." This statement was given by:

Write the drawbacks in Mendeleev's periodic table that led to its modification.