The atomic mass of silver is 107.868 amu. There are two naturally occurring isotopes of silver, Ag-107 (106.904 amu) and Ag-109 (108.905 amu). What percentage of naturally occurring silver is the heavier isotope? A. 42.5% B. 45.4% C. 48.2% D. 49.8% E. 51.8%