Question

Which is a Lewis acid?

• A. HCl
• B. \( \text{OH}^- \)
• C. \( \text{Co}^{3+} \)
• D.

Hint:

Lewis acids are substances that can accept an electron pair, and they are typically electron-deficient species like metal cations.

Answer 1

The Correct Option is C

A Lewis acid is a substance that can accept an electron pair. This definition contrasts with the Brønsted-Lowry definition of an acid as a proton donor. Lewis acids are often metal cations or molecules with an empty orbital that can accept an electron pair. 
- \( \text{HCl} \) is a Brønsted-Lowry acid, not a Lewis acid. 
- \( \text{OH}^- \) is a Lewis base because it can donate an electron pair. 
- \( \text{Co}^{3+} \), cobalt(III), is a Lewis acid because it is a metal cation with an empty orbital that can accept electron pairs. 
Thus, the correct answer is \( C \).