Question: how many protons neutrons and electrons make up an atom of nitrogen-15?
Answer: Nitrogen 15 has an atomic mass of 15. The mass number is # protons plus # of neutrons, so for N-15 mass is 15 and the protons are always 7 so there have to be 15-7=8 neutrons. N-15 has 7 electrons because it has 7 protons and p = e.