Question

Three elements X, Y and Z form a Dobereiner triad. The ratio of the atomic weight of X to that of Z is 7: 25.

If the sum of the atomic weights of X and Z is 160, find the atomic weights of X, Y and Z.

• A. X $\to$ 35, Y $\to$ 80, Z $\to$ 125
• B. X $\to$ 125, Y $\to$ 80, Z $\to$ 35
• C. X $\to$ 80, Y $\to$ 35, Z $\to$ 125
• D. X $\to$ 80, Y $\to$ 125, Z $\to$ 35

Answer 1

Answer: (A)

X $\to$ 35, Y $\to$ 80, Z $\to$ 125

Let weight of X be $7a$ $\therefore$ Atomic weight of $Z=25a$

$\therefore 7a+25a=160$

$\Rightarrow a=5$

Weight of X$=35$ and of Z is $125$

Atomic weight of Y is arranged of X and $2=\frac{35+125}{2}=80$

Hence, the correct option is $\text{A}$