Answer :
The abundance of isotope is, 10.2 %
The abundance of isotope is, 10.9 %
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:
.....(1)
Let the fractional abundance of isotope be 'x' and the fractional abundance of isotope will be 'y'
For isotope:
Mass of isotope = 23.9850 amu
Fractional abundance of isotope = 78.99 % = 0.78899
For isotope:
Mass of isotope = 24.9858 amu
Fractional abundance of isotope = x
For isotope:
Mass of isotope = 25.9826 amu
Fractional abundance of isotope = y
Average atomic mass of magnesium = 24.3050 amu
Putting values in equation 1, we get:
.............(1)
and,
.............(2)
or,
............(3)
Putting equation 3 in 1, we get:
By solving the term, we get the value of 'x'.
Now put the value of 'x' in equation 3, we get the value of 'y'.
Fractional abundance of isotope = x = 0.101839 × 100 = 10.2 %
Fractional abundance of isotope = y = 0.109171 × 100 = 10.9 %