Answer the following question given this paragraph: 

All the atoms of a given element have the same number of protons in their nucleus, but they may have different numbers of neutrons. Atoms of the same element with different numbers of neutrons are called isotopes. Many elements have one or more isotopes that are radioactive. These isotopes are called radioisotopes . Their nuclei are unstable, so they break down, or decay, and emit radiation.


Q: All the atoms of a given element have the same number of what in their nucleus, though they may have different numbers of neutrons?


A:
protons