Question

3. Atomic wt. of Cl = 35.5 and of I = 127. According to doeberiener triad rule, At. wt. of Br will be –​

Answer 1

ATOMIC WEIGHT OF Br WILL BE 35.5+127/2

=163.5/2

=81.75amu

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Answer 2

Answer:

Dobereiner triad rule :

It state that arithmetic mean of atomic masses first and third element would be approximately equal to atomic mass of second element.

If A , B and C are three element then :

Atomic mass of B is given as :

B = ( A + C ) / 2

We have given :

Atomic mass of Cl = 35.5 amu

Atomic mass of I = 127 amu

We know :

Halogen group :

F , Cl ,  Br ,  I

= > Atomic mass of Br = Atomic mass of ( Cl + I ) / 2

= > 127 + 35.5 / 2

= > 162.5 / 2

= > 81.25 amu ( Approx )

Therefore , atomic mass of Br 81.25 amu  but correct answer is 79.904 amu.