Final answer:
The atomic mass of nickel with 28 protons and 31 neutrons is 59, which is the sum of its protons and neutrons.
Step-by-step explanation:
If nickel has 28 protons and 31 neutrons, its atomic mass is the sum of the number of protons and neutrons. In this case, it is 28 protons plus 31 neutrons, which equals 59. Therefore, the correct answer is D) 59. This calculation is based on the fact that the atomic mass of an element is determined by the total number of protons and neutrons in the nucleus. The atomic number of an element, such as nickel, reflects the number of protons and defines the element. The neutron count can vary among isotopes, but for the purposes of this question, the specific number of neutrons is given to find the mass number.