Demerits of Dobereiner's Traids

Q. 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]

1. 80 u
2. 103 u
3. 88.5 u
4. 65.5 u