What was johann dobereiner’s contribution to the development of the periodic table?
1)he arranged the elements according to increasing atomic mass.
2)he arranged the elements according to increasing atomic number.
3)he identified triads of elements that had similar properties.
4)he organized elements into four groups based on their properties.

Answer;

3) He identified triads of elements that had similar properties.

Explanation;

Each of Dobereiner's triads was a group of three elements. The appearance and reactions of the elements in a triad were similar to each other.

Dobereiner discovered that the relative atomic mass of the middle element in each triad was close to the average of the relative atomic masses of the other two elements. This gave other scientists a clue that relative atomic masses were important when arranging the elements.

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