Chemistry Question on Classification of elements & periodicity in properties

Question

Among the following which one has the highest cation to anion size ratio?

Answer 1

Solution

The order of size of given cations is ${Li^{+} < Na^{+} < Cs^{+}}$ and the order of size of given anions is ${I^{-} > F^{-}}$ .
Thus, when the cation is largest and anion is smallest, the cation to anion size ratio is maximum. Hence, cation to anion size ratio is maximum for $CsF$ .