Question

$B{{F}_{3}}$ is acid according to:
(A) lewis acid
(B) Arrhenius acid
(C) Bronsted and lowry acid
(D) none of these

Answer 1

$B{{F}_{3}}$ is a halide of boron which has an incomplete octet, that is an electron-deficient species. These species tend to attract electron pairs from the donor atoms. Acids are of different types, depending upon different criteria used to determine acidity.

Complete step by step solution:
There are different types of acids depending upon different criteria used.
Lewis acids are described by the lewis theory of acid-base reactions as electron-pair acceptors. Lewis acids are chemical species which have empty orbitals and are able to accept electron pairs from electron donors. Lewis acids are electron-deficient species, which have an incomplete octet.
Arrhenius acid is a substance that dissociates in water to form hydrogen ions or protons. It increases the concentration of hydrogen ions in water.
Bronsted and Lowry acid are chemical species that give up or donate hydrogen ions during a chemical reaction.
$B{{F}_{3}}$ is a halide of boron. Boron has one electron in the valence shell and 3 fluorine atoms, therefore, it has 4 electrons in the valence shell, therefore, it has an incomplete octet, so it is electron deficient. Electron deficient species are Lewis acid. So $B{{F}_{3}}$ is a lewis acid.

Therefore, the correct answer is option (A).

Note: Boron Halides are electron-deficient species. Boron has vacant p-orbital therefore, halides like fluorine and chlorine, donate electrons to the vacant p-orbital through back bonding, therefore, it reduces electron deficiency of boron.