The atomic number of an element represents the number of protons found in the nucleus of an atom of that element. It is a unique identifier for each element on the periodic table.
The atomic number of Zn (Zinc) is 30. Therefore, the atomic number of Zn-65, which is an isotope of zinc, remains 30. Isotopes of an element have the same number of protons (atomic number) but differ in the number of neutrons.