Question

Calcium, X and Barium are the elements that can form a Dobereiner's triad. Identify the atomic weight of the element X.

[ Atomic weight of calcium = 40 u, Atomic weight of Barium = 137 u]

• A. 80 u
• B. 88.5 u
• C. 65.5 u
• D. 103 u

Answer 1

The correct option is B 88.5 u

According to the law of Dobereiner's triads, atomic weight of the second element in a triad is equal to the arithmetic mean of atomic weights of the first and the third elements in the triad.

$\therefore$ Atomic weight of X = (40 +137)/2 = 88.5 u