<u>Answer:</u> The average atomic mass of the given element is 20.169 amu.
<u>Explanation:</u>
Average atomic mass of an element is defined as the sum of masses of the isotopes each multiplied by their natural fractional abundance.
Formula used to calculate average atomic mass follows:
.....(1)
We are given:
- For isotope 1:
Mass of isotope 1 = 19.99 amu
Percentage abundance of isotope 1 = 90.92 %
Fractional abundance of isotope 1 = 0.9092
- For isotope 2:
Mass of isotope 2 = 20.99 amu
Percentage abundance of isotope 2 = 0.26%
Fractional abundance of isotope 2 = 0.0026
- For isotope 3:
Mass of isotope 3 = 21.99 amu
Percentage abundance of isotope 3 = 8.82%
Fractional abundance of isotope 3 = 0.0882
Putting values in equation 1, we get:
Hence, the average atomic mass of the given element is 20.169 amu.