Explain the following:
(a) More metal fluorides are ionic in nature than metal chlorides.
(b) Perchloric acid is a stronger acid than sulphuric acid.
(c ) Fluorine does not undergo disproportionation reactions but other halogens do.

Explanation

(a) According to Fajan's rules, a bigger anion is more easily polarised than a smaller anion by the same metal cation. `F^(Theta)` ion is smaller in size in comparison to `Cl^(Theta)` ions. Thus, the metal fluoride is more ionic than the metal chloride for the same metal cation.
(b) The oxidation state of chlorine in `HClO_(4)` is `+7` while that of `S` in `H_(2)SO_(4)` is `+6` . This `O-H` bond in `HCIO_(4)` is easily broken than in `H_(2)SO_(4)`. Hence , `HClO_(4)` is a stronger acid in comparison to `H_(2)SO_(4)`.
(c ) `F` being the most electronegative element shows only `-1` oxidation state while other halogens show both negative `(-1)` and positive `(+1,+3,+5,+7)` oxidation states. Thus, fluorine does not show disporportionation reactions but other halogens do.