Can the following groups of elements be classified as Dobereiner's triad:
`{:("(a) Na, Si, Cl"," (b) Be, Mg, Ca"):}`
Atomic mass of `Be-9, Na-23, Mg-24, Si-28, Cl-35, Ca-40.` Justify your answer in each case.

Explanation

(a) `Na, Si, Cl-`
These groups of elements cannot be classified as Dobereiner's triad as `Na,Si,Cl` have
different properties even though the atomic mass of the middle element `(Si)` is roughly
equal to the average of atomic masses of the other two elements `(Na and Cl)`.
`(23+35)/2=58/2=29,` which is nearly nearly equal to the atomic mass of `Si, i.e., 28. `
(b) `Be, Mg, Ca`
These groups of elements can be classified as Dobereiner's triad as the atomic mass of
the middle element `(Mg)` is roughly equal to the average of atomic masses of the other
two elements (Be and Ca).
`(9+40)/2=49/2=24.5,` which is nearly equal to the atomic mass of `Mg, i.e., 24.`