How many periods and groups are there in Mendeleev's periodic table?

Who stated that the properties of elements are a periodic function of their atomic number?

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

Fill in the blanks given below:
$(i)$ The first scientist to think about the properties of elements was ......... .
$(ii)$ The relationship of properties of elements suggested by Dobereiner is known as ........... .
$(iii)$ The Law of Octaves was proposed by the chemist ......... .
$(iv)$ The first periodic table was constructed by .......... and .......... .

What will be the formula of '$M$' nitrate based on the given Lothar Meyer curve?

Which elements did Mendeleev leave gaps for in his periodic table and what names did he give them?