Question

Which of these is least likely to act as a Lewis base ?

• A. CO
• B. F^-
• C. BF₃
• D. PF₃

Answer 1

The Correct Option is C

To determine which of the given options is least likely to act as a Lewis base, we need to understand what a Lewis base is. A Lewis base is a substance that can donate an electron pair. Let's analyze each option:

1. CO (Carbon monoxide): CO can act as a Lewis base because the carbon atom has a lone pair of electrons that it can donate to a Lewis acid. Therefore, CO can act as a Lewis base.
2. F^- (Fluoride ion): F^- is a negatively charged ion and has an abundance of electrons. It can easily donate an electron pair to a Lewis acid. Therefore, F^- is a strong Lewis base.
3. BF₃ (Boron trifluoride): BF₃ is a molecule where boron has an incomplete octet (is electron-deficient) and cannot donate electron pairs. Instead, it tends to accept electrons to complete its octet, making it a Lewis acid rather than a Lewis base.
4. PF₃ (Phosphorus trifluoride): PF₃ can act as a Lewis base because the phosphorus atom has a lone pair of electrons that it can donate. Thus, it can behave as a Lewis base.

From the analysis, we can conclude that BF₃ is least likely to act as a Lewis base as it is electron-deficient and tends to accept electron pairs rather than donate them. Therefore, the correct answer is:

BF₃