The acidity of BF₃ can be explained on the basis of which of the following concepts?

Lewis concept provides us with the concept of acid as the acceptor of electrons.

And this criterion for acid to be an acceptor it has to have 2 properties i. It should have a positive charge or ii. It has to have some electron deficiency to accept new electrons.

For the molecule of BF₃, it is short of an octet of electrons the central atom B has 6 electrons and is electron deficient hence, acts as a good lewis acid to fulfil its valence shell octet in spite of having no protons.

Therefore, it readily accepts lone pair of electrons from NH₃ and reacts with it.