which of these species is most likely to be a lewis acid and is also least likely to be a bronsted acid

This question is incomplete but the completed question is below

Which Of These Species Is Most Likely To Be A Lewis Acid And Is Also Least Likely To Be A Brønsted Acid? (A) NH4⁺ (B) BF₃ (C) H₂O (D) OH⁻

The correct option is B

Explanation:

A lewis acid is a substance that accepts (or is capable of accepting) a pair of electrons. For example BF₃, while a lewis base is a substance that donates (or is capable of donating) a pair of electrons. For example OH⁻.

If we take a look at the boron (B) in BF₃, it has 3 electrons on it's outermost shell, each of which are bonded to flourine and can still accept a pair of electrons (lone pair). This makes it very likely to be a lewis acid.

Bronsted lowry acid is a substance that donates or can donate a proton or H⁺ (for example HCl) while bronsted lowry base is a substance that accepts or can accept a proton or H⁺ (for example NH₃).

BF₃ cannot donate a proton or H⁺ hence it is least likely to be called a bronsted acid.