Question

what must happen to an atom of magnesium in order to become a magnesium ion mg²⁺?
it must lose two neutrons and become a different isotope.
it must gain two neutrons and become a different isotope.
it must lose two electrons and become an ion.
it must gain two electrons and become an ion.

Explanation:

An ion is formed by the gain or loss of electrons. A magnesium ion with a +2 charge ($Mg^{2 +}$) is a cation. Cations are formed when an atom loses electrons. Magnesium has an atomic number of 12 and in its neutral state has 12 electrons. To achieve a +2 charge, it must lose 2 electrons.

Answer:

It must lose two electrons and become an ion.