10 points please help

Neils bohr believed that electrons orbited the nucleus in different energy levels, based on strong support from

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?

Which characteristics can be used to differentiate star systems? check all that apply.