The correct option is B LiI
The given anions are F− and I− and the size (R) order is RF<RI
The given cations are Li+ and Cs+ and the size (R) order is RLi<RCs
For the cation to anion ratio to be minimum, the compound must have a large anion and a small cation. Here, I− is the largest anion and Li+ is the smallest cation.
Therefore, LiI has the minimum cation to anion size ratio.