Question

give advantage and disadvantage of dobereiner 's traids

Answer 1

All the then known elements could not be arranged in the form of triads.
For very low mass or for very high mass elements, the law was not holding good. Take the example of F, Cl, Br. Atomic mass of Cl is not an arithmetic mean of atomic masses of F and Br.
The only advantage of Dobereinersresearch was that it made chemists look at elements in terms of groups of elements with similar chemical and physical properties. This eventually led to rigorous classification of elements and the modern periodic table of elements, as we now know it, was discovered.
Dobereiners law of triads failed for the following reasons :
all the then known elements could not be arranged in the form of triads.
for very low mass or for very high mass elements, the law was not holding good. Take the example of F, Cl, Br. Atomic mass of Cl is not an arithmetic mean of atomic masses of F and Br.
The only advantage of Dobereiners research was that it made chemists look at elements in terms of groups of elements with similar chemical and physical properties. This eventually led to rigorous classification of elements and the modern periodic table of elements, as we now know it, was discovered.

Answer 2

advantage is that he was the first scientist to show that there was a relationship between the atomic masses of elements which acted as a source of inspiration over other scientist for further research.

disadvantage was that he could find only 3 triads which were was found to be of no use