Question

Elements x, y and z forms Dobereiner's triad. If the atomic mass of element x and z are $7$ and $39$ respectively, then what is the atomic mass of element y?

• A. $23$
• B. $46$
• C. $16$
• D. $32$

Answer 1

The correct option is A $23$

In a triad, the relative atomic mass of middle element is approximately equal to arithmatic mean of the relative atomic mass of first and third elements.
Hence the atomic mass of y $=\frac{7+39}{2}=23$