The three elements A, B and C with similar properties have atomic masses X, Y and Z respectively.The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of elements called as? Give one example of such a set of elements.

The three elements A, B and C with similar properties have atomic mass

1.	The three elements A, B and C with similar properties have atomic masses X, Y and Z respectively.The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of elements called as? Give one example of such a set of elements.
Answer» Solution :The ARRANGEMENT of these ELEMENTS is KNOWN as Dobereiner triad. Example: lithium, SODIUM and POTASSIUM.