Correct option is B
The incorrect statement is (B) if three elements are arranged in the decreasing sequence of atomic masses, then atomic mass of the third element is approximately the average of the atomic masses of the other two elements.
Explanation: Dobereiner's triads were based on the observation that when three elements with similar chemical properties are arranged in order of increasing atomic mass, the atomic mass of the middle element is approximately the average of the atomic masses of the other two elements.
Key points about Dobereiner's triads:
- Increasing order: The arrangement of elements is always in increasing order of atomic mass, not decreasing.
- Average atomic mass: The atomic mass of the middle element is roughly the average of the other two elements in the triad.
Examples:
- Li, Na, and K (alkali metals)
- Cl, Br, and I (halogens)
- Ca, Sr, and Ba (alkaline earth metals)
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