solution:
since n we know that Copper has 29 protons and 36 neutrons thus
according to the mass formula is
=number of neutrons + number of protons
=36+29
=65
therefore,
Copper has 29 protons. The mass number of an isotope is the sum of the protons and neutrons. An isotope of copper with 36 neutrons will have a mass number of 65.