(a) A, B and C are the elements of Dobereiner's triad. If the atomic mass of A is 7 and that of C is 39, what should be the atomic mass of B?
(b) Why was the Dobereiner triad discarded?
Elements A,B,C forms Dobereiner's triads. If atomic mass of element A is 7 and the atomic mass of element C is 39. Then atomic mass of element B is