# Which of the following is Dobereiner triad? Option 1) Cl, Br, I Option 2) Zn, Cr, Na Option 3) Ne, Ar, K Option 4) B, C, Si

P Plabita

As learnt in

Mendeleev's periodic table -

Mendeleev arranged the 63 discovered elements in the periodic table in to 7 horizontal rows known as periods and vertical column known as groups numbered 1 to 8.

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According to this principle, the atomic weight of the middle element in the triad is nearly the same as average of the atomic weights of other two elements.

Cl (35.5)  Br (80)  I (127)

$\frac{127 + 35.5}{2} = 81.25 \sim 80$

Option 1)

Cl, Br, I

Option 2)

Zn, Cr, Na

Option 3)

Ne, Ar, K