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

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

If silver atom is available in the form of, say, two isotopes, $_{47}\textrm{Ag}^{107}$ ($51.8$%) and $_{47}\textrm{Ag}^{109}$ ($48.2$%), calculate the average atomic mass of silver.

i. Give the formula to calculate the 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,

$105. 432 u$
$101.324 u$
$109.648 u$
$107.964 u$

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9. TBQ - Calculation of average atomic mass

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