Question

Which one is a Lewis acid?

• A. CH\(_4\)
• B. B\(_2\)H\(_6\)
• C. H\(_2\)O
• D. NH\(_3\)

Hint:

Lewis acids are electron-pair acceptors. Compounds like B\(_2\)H\(_6\) with electron-deficient atoms, such as boron, can accept electrons, making them Lewis acids.

Answer 1

The Correct Option is B

Step 1: Understand the concept of a Lewis acid
A Lewis acid is a substance that can accept an electron pair. This differs from a Brønsted-Lowry acid, which donates a proton. Lewis acids typically have a vacant orbital or can accept electron pairs from a donor.
Step 2: Analyze the given options

• CH₄ (Methane): This molecule is electron-rich and does not have a vacant orbital to accept electrons. Hence, it is not a Lewis acid.
• B₂H₆ (Diborane): This molecule has electron-deficient boron atoms with an incomplete octet, making it capable of accepting electron pairs. Therefore, B₂H₆ is a Lewis acid.
• H₂O (Water): While water can act as a Lewis base (by donating electron pairs), it is not a Lewis acid because it does not have a vacant orbital to accept electron pairs.
• NH₃ (Ammonia): Ammonia has a lone pair of electrons on nitrogen, making it a Lewis base, not an acid.

Step 3: Conclusion
The correct answer is B₂H₆, which is a Lewis acid due to its electron-deficient boron atoms that can accept electron pairs.
Conclusion:

B₂H₆ is a Lewis acid.