Question

If elements A, B and C form Dobereiner’s triad and atomic masses of A and middle element B is 40 u and 88 u respectively, then the atomic mass of element C will be

• A. 136 u
• B. 48 u
• C. 128 u
• D. 8 u

Answer 1

The correct option is A 136 u

Elements A, B and C form a Döbereiner’s triad.
$\mathrm{Atomic}\mathrm{mass}\mathrm{of}B=\frac{\mathrm{Atomic}\mathrm{mass}\mathrm{of}A+\mathrm{Atomic}\mathrm{mass}\mathrm{of}C}{2}$$88=\frac{40+\mathrm{Atomic}\mathrm{mass}\mathrm{of}c}{2}$

176 = 40 + Atomic mass of C
Atomic mass of C = 176 − 40 = 136 u
Hence, the correct answer is option (a).