(Using the energy diagram illustrate how electrons are arranged in atomic orbital Justifying why the 1st and 2nd principal quantum number electrons are filled as expected. However, from the 3rd Quantum number does not follow similar pattern​

Sally is making a model of a magnesium atom with an atomic mass number of 24 for her chemistry class. she has foam balls for the protons, neutrons, and electrons. she has added 6 neutrons to her model so far. how many more neutrons does she need to add to complete her neutral atom of magnesium?