Answer:
%abundance of isotope B-11 is 80%, therefore, the %abundance of isotope B-10 is 20%.
Step-by-step explanation:
The average atomic mass of an element is actually a weighted average atomic mass, taking into account the percent abundance of the naturally occurring isotopes of the element.
To calculate the weighted average mass, you must take the sum of atomic masses of all the naturally occurring isotopes multiplied by their %abundance.
Ave At. Mass = sum of [(isotopic mass)(%abundance)]/100
If we let the %abundance of B-11 be represented by X, then the %abundance of B-10 must be (100-X).
Now we can set up the following equation and solve for X
10.8 = [(10)(100-X) + (11)(X)]/100
1080 = 1000 - 10X + 11X
80 = X
So, the %abundance of isotope B-11 is 80%, therefore, the %abundance of isotope B-10 is 20%.