Copper has two isotopes, 63Cu and 65Cu. If the atomic mass of copper is 63.5 g/mol, what is the % of each isotope?
A 25.0 % 63Cu and 75.0 % 65Cu
B 33.0 % 63Cu and 66.0 % 65Cu
C 50.0 % 63Cu and 50.0 % 65Cu
D 66.0 % 63Cu and 33.0 % 65Cu
E 75.0 % 63Cu and 25.0 % 65Cu