the number of valence electrons the number of protons the charge of the atom the size of the atom
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: In order to determine if two atoms are copper (Cu) atoms, what must be the same for each?
Possibilities:
- the number of valence electrons
- the number of protons
- the charge of the atom
- the size of the atom

the number of protons