Answer: 268.1 u
Explanation:
Mass of isotope 1 = 267.8 u
% abundance of isotope 1 = 90.3% = [tex]\frac{90.3}{100}=0.903[/tex]
Mass of isotope 2 = 270.9 u
% abundance of isotope 2 = 9.7% = [tex]\frac{9.7}{100}=0.097[/tex]
Formula used for average atomic mass of an element :
[tex]\text{ Average atomic mass of an element}=\sum(\text{atomic mass of an isotopes}\times {{\text { fractional abundance}})[/tex]
[tex]A=\sum[267.8\times 0.903+270.9\times 0.097][/tex]
[tex]A=268.1u[/tex]
Therefore, the average atomic mass of an element is, 268.1 u
