Answer:
Atomic number of copper is 29. The atomic number of an atom is determined by the number of protons in the nucleus. Therefore, there are 29 protons in an atom of copper. In a neutral atom, there are equal number of protons and electrons. Therefore, there are 29 electrons in a copper atom. Mass number of copper is 64.
Number of protons + Number of neutrons = mass number.
Therefore, number of neutrons = 63 -29 = 35