Which of the halogen hydracids forms bi-salts ? Write reasons.

Explanation

Hydroflouric acid (HF) forms bisalt.
The Flourine atom (F) or flouride ion `(F^(-))` has a strong tendency to form hydrogen bond owing to its small size and high electronegatively . Hence, when KF is added to liquid HF, the `F^(-)` ion of KF combines with HF through hydrogen bond given biflouride ion `(HF_(2)^(-))`. Hence, `KHF_(2)` exists i.e., HF forms bi-salt. On the other hand, a relatively low electronegativity and large size of the other halogen, prevent the formation of `HX_(2)^(-)` . Hence, salts like `KHCl_(2), KHBr_(2)` and `KHI_(2)` donot exist
`KF hArr K^(+)+F^(-)`
`(F^(-)+HF to [F----H-F]^(Ө))/(KF+HF to KHF_(2))`