Question

Three elements A, B and C form a Dobereiner's triad.
The atomic mass of elements A and Care 35.5 u and
126.9 u respectively. The atomic mass of middle
element B is
​

Answer 1

Dobereiner said that the average masses of the first and the third element is equal to the second element mass .

35.5 + 126.9/2 = 76.2

Ans = Mass of Element B is 76.2