Magnesium has 3 stable isotopes with masses of 23.98504,24.98584,and 25.98259 respectively.Mg-25 is 10.13%.What are the percentages of the other two isotopes?
A)78.8% and 10.9%
B)50% and 50%
C)44.9% and 44.9%
D)83.6% and 16.4%
E)78.9% and 21.1%

Question

Quizplus · Accepted Answer

Let x% and y% be the percentages of Mg-24 and Mg-26 respectively. We know that:
x + y + 10.13 = 100 (since the total percentage of all isotopes must add up to 100)
Also, from the masses given, we know that:
(23.98504)x + (24.98584)y + (25.98259)(10.13) = 24.305
Solving these two equations simultaneously, we get:
x = 78.8% and y = 10.9%.
Therefore, the percentages of the other two stable isotopes are 78.8% for Mg-24 and 10.9% for Mg-26.

Magnesium Has 3 Stable Isotopes with Masses of 23