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

1. Dobereiner triad: A set of 3 elements with similar physical and chemical properties that is formed by the arithmetic mean of atomic masses of first and third elements gives the atomic mass of second element.

Example:

X,Y,Z is a Dobereiner triad . By adding and taking the average of atomic masses of X and Z we get the mass of Y.

$\frac{9+40}{2}=\frac{49}{2}=24.5$

Hence, the value of x is 24.5.