Answer : The average atomic mass will be closest to 35 amu.
Explanation :
Average atomic mass of an element is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.
Formula used to calculate average atomic mass follows:
[tex]\text{Average atomic mass }=\sum_{i=1}^n\text{(Atomic mass of an isotopes)}_i\times \text{(Fractional abundance})_i[/tex]
As we are given that,
Mass of isotope X-35 = 35 amu
Percentage abundance of isotope X-35 = 90 %
Fractional abundance of isotope X-35 = 0.90
Mass of isotope X-37 = 37 amu
Percentage abundance of isotope X-37 = 8.0 %
Fractional abundance of isotope X-37 = 0.08
Mass of isotope X-38 = 38 amu
Percentage abundance of isotope X-38 = 2.0 %
Fractional abundance of isotope X-38 = 0.02
Now put all the given values in above formula, we get:
[tex]\text{Average atomic mass of element}=\sum[(35\times 0.90)+(37\times 0.08)+(38\times 0.02)][/tex]
[tex]\text{Average atomic mass of element X}=35.22amu\approx 35amu[/tex]
Therefore, the average atomic mass will be closest to 35 amu.
