Question

The three imaginary elements X, Y and Z represent a Dobernener's triad. If the atomic mass of element X is 14 and that of element Y is 46, then the atomic mass of element Z will be:

(a) 28
(b) 60
(c) 78
(d) 72

Answer 1

(c) 78
The atomic mass of the element Z is 78.
According to Dobereiner's law of triads, atomic mass of $\mathrm{Y}=\frac{\mathrm{X}+\mathrm{Z}}{2}$
Substituting the atomic masses we get:

$46=\frac{14+\mathrm{Z}}{2}$

$92=14+\mathrm{Z}$

Therefore, $\mathrm{Z}=78$.