Question

Amongst the given options which of the following molecules/ion acts as a Lewis acid?

• A. H₂O
• B. BF₃
• C. OH^-
• D. NH₃

Answer 1

The Correct Option is B

To determine which molecule or ion acts as a Lewis acid among the given options, we need to understand the concept of a Lewis acid. A Lewis acid is a chemical species that can accept an electron pair. In other words, it is an electron-pair acceptor.

Let's analyze each option:

1. H₂O: Water is a polar molecule with a bent shape. It has two lone pairs of electrons. It typically acts as a Lewis base (an electron-pair donor) because it can donate these lone pairs to other species.

2. BF₃: Boron trifluoride is a molecule with boron at the center bonded to three fluorine atoms. Boron has only six electrons in its valence shell in this molecule, making it electron-deficient. It can accept an electron pair to complete its octet, thus acting as a Lewis acid.

3. OH^-: The hydroxide ion has a lone pair and a negative charge. It has an excess of electrons and generally acts as a Lewis base by donating its lone pair to an electron-pair acceptor.

4. NH₃: Ammonia has a lone pair of electrons on the nitrogen atom. It commonly acts as a Lewis base by using this lone pair to form bonds with Lewis acids.

Based on the analysis above, the correct answer is BF₃ because it can accept an electron pair to complete its octet, classifying it as a Lewis acid.