Question

Elements A,B,C forms Dobereiner's triads. If atomic mass of element A is 7 and the atomic mass of element C is 39. Then atomic mass of element B is

• A. 46
• B. 23
• C. 53
• D. 11

Answer 1

The correct option is B

23

Answer: Option (B)

Explanation of correct option.

Dobereiner gave the first method of classification in which he chooses the group of three elements called triads. He arranged the three elements in order of increasing atomic masses in such a way the atomic mass of the middle element is the arithmetic mean of the top and bottom elements

. For example Li, Na, K.

• Mass of Li = 7
• Mass of Na = 23
• Mass of K= 39

Therefore, Mass of Na = $\frac{\mathrm{Mass}\mathrm{of}\mathrm{Li}+\mathrm{Mass}\mathrm{of}\mathrm{K}}{2}$

Mass of Na = $\frac{7+39}{2}$ = 23

Hence, Li, Na, and K are Dobereiner's triads.

Hence, option (B) is correct.