Some groups of three elements are given below: Which of these groups is not an example of Dobereiner's triad ? Explain it.

Some groups of three elements are given below: Which of these group

1.	Some groups of three elements are given below: Which of these groups is not an example of Dobereiner's triad ? Explain it.
Answer» SOLUTION :For group .A. : <BR> Average of ATOMIC masses of N and As `=(14+74.9)/(2)=44.45u` This average VALUE is not equal to the actual atomic mass of the middle ELEMENT phosphorus (P). Therefore, these three elements do not form a Dobereiner.s triad. For group .B. : Average of atomic masses of Ca and Ba `=(40.1+137.3)/(2)` =88.7u This average value is approximately equal to the atomic mass of the middle element strontium (Sr). Therefore, these three elements form a Dobereiner.s triad. For group .C. : Average of atomic masses of Cl and I `=(35.5+126.9)/(2)` =81.2u This average value is approximately equal to the mass of the middle element bromatomic ine (Br). Therefore, these three elements form a Dobereiner.s triad.