Question

Which of the following can be classified as Dobereiner's triads?

(a) P, As, Sb

(b) Cu, Ag, Au

(c) S, Se, Te

• A. a and b
• B. b and c
• C. a and c
• D. all of the above

Answer 1

The correct option is C a and c

a) $P\left(31u\right),As\left(74.9u\right),Sb\left(122u\right)$ and (d) $S\left(32u\right),Se\left(79u\right),Te\left(127.6u\right)$ represent Dobereiners triad.

According to the law of triad proposed by Dobereiners, the atomic weight of a middle element is nearly the same as the average of the atomic weights of the other two elements.

a) $\frac{31+122}{2}=76.5\simeq 74.9u$

d) $\frac{32+127.6}{2}=79.8\simeq 79u$