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Q.
Which of the following has the highest cation to anion size ratio?
Classification of Elements and Periodicity in Properties
Solution:
The cation to anion size ratio will be maximum when the cation is of largest size and the anion is of smallest size. Among the given species, $Cs^+ $ has maximum size among given cations and $F^-$ has smallest size among given anions, thus $CsF$ has highest $r_c/r_a $ ratio