Question

Which of the following can form Dobereiner's Triads with Li(A = 6.9) and sodium (A = 23)?

• A. K (A = 32)
• B. K (A = 37)
• C. K (A = 45)
• D. K (A = 39)

Answer 1

The correct option is D

K (A = 39)

By looking at the atomic masses of given elements, you can tell that they are the first two elements of the triad. Thus 23 is the average mass. If you try with the given options, you will find that only K (m = 39) will satisfy Doberenier's law of triads.