Atomic number of copper is:

29

The correct answer is option 4. 29.

The atomic number of an element is the number of protons found in the nucleus of an atom of that element. It uniquely identifies each element on the periodic table.

For copper (Cu), the atomic number is 29. This means that every atom of copper contains 29 protons in its nucleus. In a neutral atom, the number of protons equals the number of electrons surrounding the nucleus.

The atomic number of an element also determines its position on the periodic table. Since copper has 29 protons, it is located in the 29th position on the periodic table.

In summary, the atomic number of copper is 29, indicating that every atom of copper contains 29 protons in its nucleus.