Copper has two naturally occurring isotopes: Cu-63 and Cu-65. Cu-63 has a natural abundance of 69.15%. Calculate the mass of Cu-63 if the mass ratio of the two isotopes is 1.0318.

• A. 64.93 amu
• B. 62.93 amu
• C. 63.15 amu
• D. 63.55 amu

Answer: (B)