Can the following groups of elements be classified as Dobereiner's triad?
$(a)$ $Na, Si, Cl$
$(b)$ $Be, Mg, Ca$
Atomic mass of $Be = 9, Na = 23, Mg = 24, Si = 28, Cl = 35, Ca = 40$. Explain by giving reasons.

(B) No,because these elements do not possess similar chemical properties,which is a fundamental requirement for Dobereiner's triads,even though the atomic mass of silicon $(28)$ is approximately the average of the atomic masses of sodium $(23)$ and chlorine $(35)$,i.e.,$(23 + 35) / 2 = 29$.
$(b)$ Yes,because these elements belong to the same group (alkaline earth metals) and exhibit similar chemical properties. Furthermore,the atomic mass of magnesium $(24)$ is the average of the atomic masses of beryllium $(9)$ and calcium $(40)$,i.e.,$(9 + 40) / 2 = 24.5$,which is very close to $24$.