Question

Based on Dobereiner's theory of triads, match the following.
Element (atomic mass)

• A. X : Br
• B. Y: Na
• C. Z: Sr

Answer 1

Dobereiner proposed that when three elements in a triad are written in the order of increasing atomic masses; the atomic mass of the middle element is roughly the average of the atomic masses of the other two elements.
For example,
A = $\frac{35.5+126.9}{2}$
A = 81.2
As, atomic mass of Bromine (Br) is 79.9 which is roughly close to the atomic mass calculated, we can say that X = Br.