a. Cobalt atoms always have 27 protons (see periodic table). The mass number is the total number of protons and neutrons, so Co-59 has 32 neutrons, and Co-60 has 33. b. The number of orbiting electrons in a neutral atom matches the number of protons, i.e., the atomic number. Neutral cobalt atoms have 27 electrons.
Work Step by Step
This is discussed on pages 215 and 218.