Question

What was Dobereiner's contribution to the evolution of the periodic table?

Answer 1

Dobereiner is the first one to contribute in the evolution of the periodic table. He arranged the then known elements of the periodic table as a group of three elements and he called this group as traids. He arranged the elements in such a way that the average of the masses of the first and third element will be equal to the atomic mass of the middle one.
for e.g.,
lithium,sodium and potassium.
atomic mass of lithium+mass of potassium/2 = 22
i.e.,6+38/2=22 .
and the atomic mass of sodium is 22.

Answer 2

hii

the first one is right so it is correct