The internuclear distance is the sum of the ionic radii of the cation and the anion ($d = r_+ + r_-$). To maximize this distance, we need the largest cation and the largest anion.

1. Cations: Cs is in Group 1 (Alkali metals), Period 6. Li is in Group 1, Period 2. Atomic/ionic size increases down a group. Therefore, $r(Cs^+) > r(Li^+)$.
2. Anions: I is in Group 17 (Halogens), Period 5. F is in Group 17, Period 2. Atomic/ionic size increases down a group. Therefore, $r(I^-) > r(F^-)$.

Comparing the combinations:

• CsI: Largest cation ($Cs^+$) + Largest anion ($I^-$) $\rightarrow$ Maximum internuclear distance.
• LiF: Smallest cation ($Li^+$) + Smallest anion ($F^-$) $\rightarrow$ Minimum internuclear distance.

Therefore, CsI has the maximum internuclear distance.