Copper has two naturally occurring stable isotopes, $C_{29}{u}^{63}$ and $C_{29}{u}^{65}$. Which statement correctly compares these two isotopes?

• A. They have different numbers of protons but the same number of neutrons.
• B. They have the same numbers of protons and neutrons but different numbers of electrons.
• C. They have the same number of protons but different numbers of neutrons.
• D. They have different numbers of protons and different chemical properties because they are different elements.

Answer: (C)