Introduction:
Ionic bonds are formed between metal and nonmetal ions. The stability of an ionic bond depends on the balance between the attractive forces between the opposite charges and the repulsive forces between the like charges.

Explanation:
To determine the most stable ionic bond, we need to consider the charges and sizes of the ions involved.

Ion Charges:
- Na (sodium) has a +1 charge.
- Cl (chlorine) has a -1 charge.
- Mg (magnesium) has a +2 charge.
- F (fluorine) has a -1 charge.
- Li (lithium) has a +1 charge.

Ion Sizes:
- Na+ and Mg2+ have larger radii compared to Li+ and F-, as they have more electrons and are located in higher periods of the periodic table.
- Cl- has a larger radius compared to F-, as it is located in a higher period of the periodic table.

Attractions and Repulsions:
The stability of an ionic bond depends on the balance between the attractive forces between the opposite charges and the repulsive forces between the like charges.

Na+ and Cl-:
- Na+ has a +1 charge and Cl- has a -1 charge, resulting in a strong attractive force between the two ions.
- The repulsive forces between the like charges are relatively small, as the Na+ and Cl- ions have different sizes.
- Therefore, the ionic bond between Na+ and Cl- is relatively stable.

Mg2+ and F-:
- Mg2+ has a +2 charge and F- has a -1 charge, resulting in a stronger attractive force compared to Na+ and Cl-.
- However, the repulsive forces between the like charges are larger, as Mg2+ and F- ions have similar sizes.
- The higher charge on the Mg2+ ion also increases the repulsive forces between the two ions.
- Therefore, the ionic bond between Mg2+ and F- is less stable compared to Na+ and Cl-.

Li+ and F-:
- Li+ has a +1 charge and F- has a -1 charge, resulting in a strong attractive force between the two ions.
- The repulsive forces between the like charges are relatively small, as Li+ and F- ions have different sizes.
- However, the smaller size of Li+ ion compared to Na+ makes the repulsive forces slightly larger.
- Therefore, the ionic bond between Li+ and F- is less stable compared to Na+ and Cl-.

Conclusion:
Among the given options, the most stable ionic bond is formed between Mg2+ and F- ions. This is because the attractive forces between the opposite charges are stronger, but the repulsive forces between the like charges are larger due to similar sizes and higher charge on the Mg2+ ion.