Question

A, B and C are the elements of a Dobereiner's triad. If the atomic mass of A is 10 u and that of C is 28 u, what should be the atomic mass of B?

• A. 24 u
• B. 19 u
• C. 29 u
• D. 34 u

Answer 1

The correct option is B 19 u

• We know that the law of triads says that the mass of the second element should be the mean or average of the masses of the first and third ones.
• A, B and C belong to Dobereiner’s triad, the atomic mass of A given is 10 u and the atomic mass of C given is 28 u
• Thus, the atomic mass of B = $\frac{(\mathrm{Atomic}\mathrm{maass}\mathrm{of}A+\mathrm{Atomic}\mathrm{mass}\mathrm{of}C)}{2}$
• Atomic mass of B =$\frac{(10+28)}{2}$= 19 u.