Chlorine, bromine and iodine form a Dobereiner's triad . Chlorine has atomic mass 35.5 and iodine has atomic mass 126.9 . Predict the atomic mass of bromine.

Explanation

As chlorine (CI), bromine (Br) and iodine (I) form a triad, atomic mass of Br should be the mean of atomic masses of CI and I .
`therefore` Atomic mass of Br` = (35.5+126.9)/(2)=81.2`
`therefore` Atomic mass of Br would be approximately 81 (actual mass is 79.9).