Question

Magnesium has three isotopes. Magnesium-24 has a percent abundance of 78.99% Magnesium- 26 has a percent abundance of 11.01% What is the percent abundance of mangesium- 25

Answer 1

78.99% + 11.01% = 90%
100% - 90 % = 10%

Answer 2

and how did you come up with that answer

Answer 3

from your problem:
Magnesium-24 has a percent abundance of 78.99%
Magnesium- 26 has a percent abundance of 11.01%
Just how many % is left in the whole?

Answer 4

Magnesium - isotope 24 - isotope 26 = 10% left over for isotope 25

Answer 5

they have to add up to 100%, you have 10.00% left over to play with.