Write a note on the genesis of the periodic table.

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

Given below are two statements :
Statement $(I):$ According to the Law of Octaves,the elements were arranged in the increasing order of their atomic number.
Statement $(II) :$ Meyer observed a periodically repeated pattern upon plotting physical properties of certain elements against their respective atomic numbers.
In the light of the above statements,choose the correct answer from the options given below :

Which of the following is a Dobereiner's triad?

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 ............ .

The law of triads is applicable to a group of