TBQ - Calculation of average atomic mass — task. Chemistry CBSE Live product, Class 9 (2026-27).

Give the average atomic mass of an element from its isotopes:

If bromine atom is available in the form of, say, two isotopes, $_{35}\textrm{Br}^{79}$ ($49.7$%) and $_{35}\textrm{Br}^{81}$ ($50.3$%), calculate the average atomic mass of bromine.

i. What is the formula to determine tha average atomic mass?

\frac{\sum (Mass of isotopes \times % Natural abundance)}{100}

\frac{\sum (Mass of isotopes \times 100)}{% Natural abundance}

\frac{(% Natureal abundance \times 100)}{\sum (Mass of isotopes)}

d. $\frac{\sum (Mass of isotopes)}{100}$

ii. When substituting the given values in the formula, we get,

$77.0366 u$
$80.006 u$
$90.072 u$
$92.7346 u$

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9. TBQ - Calculation of average atomic mass

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