Answer :
Answer: The average atomic mass of an element is 35.67 amu and the unknown element will be chlorine.
Explanation:
Mass of isotope 1 = 34.969 amu
% abundance of isotope 1 = 64.88% = [tex]\frac{64.88}{100}=0.6488[/tex]
Mass of isotope 2 = 36.966 amu
% abundance of isotope 2 = (100-64.88)% = [tex]\frac{100-64.88}{100}=0.3512[/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[34.969\times 0.6488)+(36.966 \times 0.3512]][/tex]
[tex]A=35.67amu[/tex]
Therefore, the average atomic mass of an element is 35.67 amu and the unknown element will be chlorine.