Question

When a Dobereiner triad is considered, the sum of atomic weights of extreme elements X and Z is 177.6 and difference of Z and Y is five times the number of protons present in a neon atom. Identify X, Y and Z.

• A. $X\to Ca,Y\to Sr,Z\to Ba$
• B. $X\to Li,Y\to Na,Z\to K$
• C. $X\to K,Y\to Rb,Z\to Cs$
• D. $X\to Sr,Y\to Ba,Z\to Ra$

Answer 1

The correct option is A $X\to Ca,Y\to Sr,Z\to Ba$

The atomic weight of Y is avergae of X and Z

$\therefore M_Y=\frac{177.6}{2}=88.8$

$88.8$ is weight of Sr. So Y is Sr. According to this only option A is correct.