Final answer:
The symbol Mg2+ denotes a magnesium ion with a 2+ charge, which forms stable ionic bonds with other negatively charged ions, such as the two chloride ions in magnesium chloride (MgCl2).
Step-by-step explanation:
The symbol Mg2+ refers to a magnesium ion with a positive charge of two. This indicates that the magnesium atom has lost two electrons to achieve a stable electron configuration, usually when forming an ionic bond with other ions. For example, in the compound MgCl2, the magnesium ion combines with two chloride ions (Cl-) because each chloride ion has a charge of 1-. Therefore, two chloride ions are required to balance out the 2+ charge of a single magnesium ion, leading to the formation of magnesium chloride, MgCl2.