Answer:
One atom of Al has 13 protons and 14 neutrons.
Step-by-step explanation:
Al 27 13 Al
27 is the atomic mass. One atom of aluminum has an atomic mass of 27, which consists of protons (1 mass unit each), neutrons (1 mass unit each) and electrons (0 mass units each).
13 is the atomic number. It is the number of protons in the nucleus. An element is defined as the number of protons. As long as there are 13 protons, it will be aluminum regardless of the numbers of neutrons (isotopes) or electrons (ions).
(27 - 13) = 14 neutrons, since protons are 1 each (13 total) and electrons are 0 each. Al can also exist as 28 13 Al. It still has 13 protons, but now has 15 neutrons (28 - 13) = 15.