Final answer:
The percent abundance of magnesium-24 and magnesium-26 is 78.83% and 11.17% respectively.
Step-by-step explanation:
In order to find the percent abundance of magnesium-24 and magnesium-26, we need to use the given information about the percent abundances and masses of the isotopes. Let's start with magnesium-24. We are told that it has a mass of 23.985 amu, but we are not given its percent abundance. However, we know that the total percent abundance of all three isotopes must add up to 100%. So, if we subtract the percent abundances of magnesium-25 and magnesium-26 (10.00% and 11.17% respectively) from 100%, we can find the percent abundance of magnesium-24. Subtracting 10.00% and 11.17% from 100% gives us 78.83%, which is the percent abundance of magnesium-24.
Next, we can find the percent abundance of magnesium-26 using the same method. Subtracting the percent abundances of magnesium-24 and magnesium-25 (78.83% and 10.00% respectively) from 100% gives us 11.17%, which is the percent abundance of magnesium-26.