Question

dobereiner noted triads of elements. what was important about the triads? the middle element was significantly more reactive than the lighter or the heavier of the triad. the elements had three different chemical properties. the reactivity of the elements in any given triad were distinctly different. the middle element had a mass approximately half - way between the lighter and heavier of the triad.

Explanation:

Dobereiner's triads were groups of three elements where the atomic mass of the middle - element was approximately the arithmetic mean of the atomic masses of the other two elements.

Answer:

The middle element had a mass approximately half - way between the lighter and heavier of the triad.