Question

Lithium, sodium and potassium form a Dobereiner's triad. The atomic masses of lithium and potassium are 7 and 39 respectively.

Answer 1

the atomic mass of sodium will be 39+7/2
=23.

Answer 2

There fore according to dobereiners triads, the mass of sodium is the average of masses of lithium and pottasium=(7+39)÷2=23