Why is `SIF_(4)` a stronger Lewis acid a s compared to `SiCl_(4)`?

Explanation

Silicon atom has 3d vacant orbitals and can take up electron s from elecron donor species not can extend its oxidant state of +6. Therefore, it can behave as a Lewsis acid Now. `F^(-)` ion is a strnger Lewis base than `Cl^(-)` ion. Therefore `SiF_(4)` can easily accept two `F^(-)` ion and from `[FiF_(6)]^(2-)` ion.

It is quite difficult for `SiCl_(4)` ions to take up two `Cl^(-)` ions to form `(SiCl_(6))^(2-)` ion.