2. Atoms and the Periodic Table

Which of the following choices has the greatest atomic mass?

Only three isotopes of magnesium exist on earth. ²⁴Mg is the most common form at 78.70% natural abundance with a mass of 23.98504 amu, ²⁵Mg has a 10.13% natural abundance, while ²⁶Mg has a natural abundance of 11.17% and a mass of 25.98259 amu. What is the mass of the ²⁵Mg isotope?

Silver has two naturally occurring isotopes: Ag-107 and Ag-109. The Ag-109 isotope has an isotopic mass of 108.905 amu and a natural abundance of 48.16%. What is the isotopic mass of Ag-107? The atomic mass of silver is 107.868 amu).