Which of the following is a Dobereiner triad?

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 modern periodic table is based on the atomic number of the elements. The experiment which proved the significance of the atomic number was:

Name the scientists who contributed to the development of the periodic table and state their respective laws or contributions.

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

Why do we need to classify elements?