Final answer:
The most common isotope of magnesium is Mg-24 due to its highest percentage abundance of 78.70%. To determine the average atomic mass, each isotope's mass is multiplied by its abundance percentage and added together.
Step-by-step explanation:
The most common isotope of magnesium can be determined by comparing the isotopes' mass percentages to their respective atomic masses. Magnesium has three common isotopes - Mg-24, Mg-25, and Mg-26. Given that a sample of magnesium contains 78.70% of Mg-24 atoms with a mass of 23.98 amu, 10.13% of Mg-25 atoms with a mass of 24.99 amu, and 11.17% of Mg-26 atoms with a mass of 25.98 amu,
we can calculate the average atomic mass. Since Mg-24 has the highest percentage abundance, we can infer that it is the most common isotope. To calculate the average atomic mass, multiply each isotope's mass by its corresponding percentage (expressed as a decimal), then sum these values:
- (78.70/100) × 23.98 amu + (10.13/100) × 24.99 amu + (11.17/100) × 25.98 amu
- This calculation will yield the average atomic mass of magnesium, reflecting the relative abundance of its isotopes.