Question

Which among the following acts as a Lewis acid? \[ A) \text{AlCl}_3, \quad B) \text{NH}_3, \quad C) \text{OH}^-, \quad D) \text{H}_2\text{O} \]

• A. AlCl$_3$
• B. NH$_3$
• C. OH$^-$
• D. H$_2$O

Hint:

A Lewis acid is an electron pair acceptor, while a Lewis base is an electron pair donor.

Answer 1

The Correct Option is A

A Lewis acid is a substance that can accept a pair of electrons. Let's analyze the options:

1. Step 1: Understand Lewis acids. - AlCl$_3$: Aluminum chloride acts as a Lewis acid because aluminum has an incomplete octet and can accept electron pairs from a donor, such as a lone pair of electrons from another molecule. Therefore, AlCl$_3$ is a Lewis acid. - NH$_3$: Ammonia has a lone pair of electrons on nitrogen, making it a Lewis base, not an acid. - OH$^-$: Hydroxide is a Lewis base because it can donate a lone pair of electrons, not accept them. - H$_2$O: Water has lone pairs on oxygen, making it a Lewis base, not an acid. Thus, the correct Lewis acid is AlCl$_3$.