Answer:
Co-59 and Co-60 differ in the number of neutrons.
Step-by-step explanation:
Co-59 and Co-60 are isotopes of one another. Isotopes differ from one another as they have different mass number but same atomic number. Mass number is the sum of the number of protons and neutrons. As they have the same atomic number they have same number of protons. They have different number of neutrons.
Co has atomic number 27. So Co-59 and Co-60 have (59-27) or 32 and (60-27) or 33 number of neutrons respectively.