Question

If three elements X. Y and Z form a triad and atomic weights of X and Z are $9$ and $40$, respectively, then the atomic weight of an element Y is

Answer 1

Dobereiner triad:

1. The atomic weight of the center element of the triad, according to Dobereiner, is the arithmetic mean of the atomic weights of the other two components.
2. Dobereiner traid was first discovered in 1817. It is comprised of alkaline earth metals i.e, calcium, strontium, and barium.

• Atomic weight of Y $$\begin{gathered} =\frac{9+40}{2} \\ =24.5g \end{gathered}$$

Therefore, If three elements X. Y and Z form a triad and atomic weights of X and Z are $9$ and $40$, respectively, then the atomic weight of an element Y is $24.5g$.