Copper has two isotopes. The one isotope (Copper-63) has an abundance of 69.2% and a mass of 62.930 amu. The second isotope (Copper-65) has an abundance of 30.8% and a mass of 64.928 amu. Calculate the average atomic mass of copper. 62.930 amu 63.545 amu 63.929 amu 64.928 amu