Final answer:
The most abundant isotope of Mg is 24Mg, as it constitutes 78.70% of a magnesium sample, which is the highest percentage, and its mass is closest to the relative atomic mass of magnesium at 24.3 amu.
Step-by-step explanation:
To determine the most abundant isotope of Mg, we should look at the relative atomic mass of magnesium and the given isotopic masses and abundances. The relative atomic mass of magnesium is 24.3, which hints that the most abundant isotope must have a mass close to this value.
Given the data:
- 78.70% of 24Mg atoms (mass 23.98 amu)
- 10.13% of 25Mg atoms (mass 24.99 amu)
- 11.17% of 26Mg atoms (mass 25.98 amu)
The most abundant isotope of Mg can be found by acknowledging that the abundant mass percentage is closest to the relative atomic mass.
In this case, 24Mg has the highest percentage and is nearest to the average atomic mass of magnesium (24.3 amu) which makes it the most abundant isotope. Therefore, the correct answer is (a) 24Mg.