Answer : The average atomic mass of an element is, 268.6 amu.
Solution : Given,
Mass of isotope 1 = 267.8 amu
% abundance of isotope 1 = 87.8% = 0.878
Mass of isotope 2 = 269.9 amu
% abundance of isotope 2 = 12.2% = 0.122
Formula used for average atomic mass of an element :
\(\text{ Average atomic mass of an element}=\sum(\text{atomic mass of an isotopes}\times {{\text { fractional abundance}})\)
\(\text{ Average atomic mass of an element} Y=\sum[(267.8\times 0.878)+(269.9\times 0.122)\)
\(\text{ Average atomic mass of an element}=268.06amu\)
Therefore, the average atomic mass of an element is, 268.6 amu.
