In order to determine if two atoms are copper (Cu) atoms, which property must they have in common?

• A. The same atomic mass
• B. The same number of neutrons
• C. The same number of electrons
• D. The same number of protons

Answer: (D)

Verified step by step guidance

1. Understand that an element is defined by its atomic number, which is the number of protons in the nucleus of its atoms.
2. Recognize that copper (Cu) atoms must have the same number of protons to be identified as copper, regardless of differences in neutrons or electrons.
3. Note that atomic mass can vary due to different numbers of neutrons (isotopes), so having the same atomic mass is not necessary for atoms to be the same element.
4. Understand that the number of electrons can change if the atom is ionized, so it is not a defining property of the element itself.
5. Conclude that the key property two atoms must share to both be copper atoms is having the same number of protons.