`AlF_(3)` is insoluble in anhydrous `HF` but dissolves on addition of `NaF. AlF_(3)` precipitates out of the resulting solution when gaseous `BF_(3)` is bubbled through. Give reasons.

Explanation

Anhydrous `HF` is stabilised due to intermolecular H-bonding and is less dissociated. `AlF_(3)` is soluble in `HF` in the presence of `KF` due to the formation of `[AlF_(6)]^(3-)`.
`3KF + AlF_(3) to K_(3)[AlF_(6)]`
`BF_(3)` displaces `F^(Ө)` from `[AlF_(6)]^(3-)` because it is more acidic than `AlF_(3)`.
`K_(3)[AlF_(6)] + BF_(3) to AlF_(3) darr + 3KBF_(4)`.