Answer is: B) They all have the same number of electrons.
1) ²⁰NeAtomic number of neon is 10, mass number is 20:
Neon have 10 protons, 10 electrons (atomic number) and 10 neutrons (mass number - atomic number).
2) F⁻¹
Fluorine have atomic number 9.
Fluorine have 9 protons (atomic number) and 10 electrons (9 +1).
3) Mg²⁺
Magnesium have atomic number 12.
Magnesium have 12 protons and 10 electrons (12-2).
