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Among the following which one has the highest cation to anion size ratio?
A
CsI
B
CsF
C
LiF
D
NaF
Detailed Solution
The ratio $\frac{r_{cation}}{r_{anion}}$ is highest when the cation is the largest and the anion is the smallest.
Cation sizes: $Li^+ < Na^+ < Cs^+$, so $Cs^+$ is the largest cation.
Anion sizes: $F^- < I^-$, so $F^-$ is the smallest anion.
The combination of the largest cation with the smallest anion is CsF.
Hence CsF has the highest cation to anion size ratio.
Cation sizes: $Li^+ < Na^+ < Cs^+$, so $Cs^+$ is the largest cation.
Anion sizes: $F^- < I^-$, so $F^-$ is the smallest anion.
The combination of the largest cation with the smallest anion is CsF.
Hence CsF has the highest cation to anion size ratio.