In order to determine if two atoms are copper (CU) atoms, what must be the same for each? the number of valence electrons
the number of protons
the charge of the atom
the size of the atom

A

Explanation:

Two atoms of the same element can be different if their electrons are in different states. If one copper atom has an electron in an excited state and another copper atom has all of its electrons in the ground state, then the two atoms are different.