Final answer:
The ionic bond in MgO is predicted to be stronger than in NaF, due to the double charge on both Mg and O ions compared to the single charge on Na and F ions, which leads to a higher lattice energy indicated by a similar structure and ion radii.
Step-by-step explanation:
The strength of an ionic bond is influenced by the charge on the ions involved and their radii. The lattice energy, which is a measure of the strength of the bonds in an ionic solid, tends to increase with the charge of the ions and decrease as the ions get larger. Given the options (a) Mg−O and (b) Na−F, we can predict that MgO would have a stronger ionic bond than NaF. This is because both the magnesium (Mg2+) and oxygen (O2−) ions have double the charge of the sodium (Na+) and fluoride (F−) ions in NaF. Additionally, based on the fact that ionic compounds with ions of higher charges and similar radii have larger lattice energies (as shown with a lattice energy of 4008 kJ/mol for MgO versus that of LiF), we can extrapolate that MgO would have a stronger bond due to the quadrupling of energy expected as a result. As both Mg2+ and O2− have double the charge and similar ionic radii to Na+ and F−, the prediction is that MgO would have a significantly larger lattice energy, and therefore a stronger bond than NaF.