Which of the following pairs will form the most stable ionic bond?

Stable ionic bond is formed when lattice energy is high.

Lattice energy $$\begin{gathered} \propto \frac{1}{\mathrm{Size} \mathrm{of} \mathrm{cation} \mathrm{and} } \\ \propto \frac{1}{\mathrm{Size} \mathrm{of} \mathrm{anion}} \\ \propto \mathrm{Charge} \mathrm{of} \mathrm{the} \mathrm{ion} \end{gathered}$$

  Na⁺ and F^- form strong ionic bond.