A, B and C are the elements of a 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?

As per Dobereiner’s triad, the atomic mass of the middle element is the average of the atomic mass of first and third element.

Given,

Mass of A = 7

Mass of C = 39

Mass of B = (7+39)/2 = 23