The law of triads is applicable to a group of

Which important property did Mendeleev use to classify the elements in his periodic table and did he stick to that?

The atomic masses of $Cl$ and $I$ are $35.5$ and $127$ respectively. According to Dobereiner's law of triads,the atomic mass of $Br$ will be ............ .

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.

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.

Mendeleev's periodic law states that the properties of elements are a periodic function of their