Answer: Atomic mass of the element E is 281.73 amu.
Explanation: We are given an element E, having 3 isotopes.
Atomic mass of the element is calculated by:
[tex]\text{Atomic mass of the element}=\sum_{i=1}^n(\text{Mass of isotope})_i(\text{Fractional abundance})_i[/tex] .....(1)
Fractional abundance can be calculated by:
[tex]\text{Fractional abundance}=\frac{\text{Percentage abundance}}{100}[/tex]
Mass of isotope 1 = 278 amu
Fractional abundance of isotope 1 =[tex]\frac{25}{100}[/tex] =0.25
Mass of isotope 2 = 281 amu
Fractional abundance of isotope 2 = 0.38
Mass of isotope 3 = 285 amu
Total fractional abundance = 1
Fractional abundance of isotope 3 = 1 - (0.25+0.38) = 0.37
Putting all the values in equation 1, we get
[tex]\text{Atomic mass of the element}=\left[(278\times 0.25)+(281\times 0.38)+(285\times 0.37) \right ][/tex]
Atomic mass of the element E = 281.73 amu.
