Which one is Lewis acid

Options

A. `Cl^(-)`
B. `Ag^(+)`
C. `C_(2)H_(5)OH`
D. `S^(2-)`

Explanation

To determine which one is a Lewis acid from the given options, we first need to understand the definition of a Lewis acid. A Lewis acid is defined as a substance that can accept a pair of electrons (electron pair acceptor). In contrast, a Lewis base is a substance that can donate a pair of electrons (electron pair donor).

Now, let's analyze the options provided:

1. **Cl⁻ (Chloride ion)**:
- The chloride ion has a full octet and possesses lone pairs of electrons. It can donate these lone pairs, which means it acts as a Lewis base, not a Lewis acid.

2. **Ag⁺ (Silver ion)**:
- The silver ion has vacant orbitals available. This means it can accept a pair of electrons from a Lewis base. Therefore, Ag⁺ qualifies as a Lewis acid.

3. **C₂H₅OH (Ethanol)**:
- In ethanol, the oxygen atom has lone pairs of electrons and can donate these electrons. Hence, ethanol acts as a Lewis base, not a Lewis acid.

4. **S²⁻ (Sulfide ion)**:
- The sulfide ion also has lone pairs of electrons that it can donate. Thus, it is a Lewis base.

Based on this analysis, the only option that acts as a Lewis acid is **Ag⁺ (Silver ion)**.

### Final Answer:
The Lewis acid among the given options is **Ag⁺ (Silver ion)**.