Here's how to determine the number of protons in a Co-60 atom:

* The Atomic Number: The number of protons in an atom defines its element. The atomic number of cobalt (Co) is 27.

* Isotopes: The "60" in Co-60 refers to the atom's mass number, which is the sum of protons and neutrons. While the number of neutrons can vary (creating isotopes), the number of protons always remains the same for a given element.

Therefore, an atom of Co-60 has 27 protons.