Which of the following is not a base ?

Options

A. KOH
B. ZnO
C. `Al(OH)_(3)`
D. NaCl

Explanation

To determine which of the following options is not a base, we can analyze each option based on their chemical properties and behavior in aqueous solution.

### Step-by-Step Solution:

1. **Understanding Bases**:
- A base is a substance that can accept protons (H⁺ ions) or donate hydroxide ions (OH⁻) in an aqueous solution.

2. **Analyzing the Options**:
- **Option 1: KOH (Potassium Hydroxide)**
- KOH is a strong base that dissociates in water to produce K⁺ and OH⁻ ions. Therefore, KOH is a base.

- **Option 2: ZnO (Zinc Oxide)**
- ZnO is an amphoteric oxide, meaning it can react with both acids and bases. It can produce OH⁻ ions when reacting with acids, thus behaving as a base in those reactions. Therefore, ZnO can be considered a base.

- **Option 3: Al(OH)₃ (Aluminum Hydroxide)**
- Al(OH)₃ dissociates in water to produce Al³⁺ and OH⁻ ions. Since it produces OH⁻ ions, Al(OH)₃ is also a base.

- **Option 4: NaCl (Sodium Chloride)**
- NaCl is a neutral salt formed from the reaction of a strong acid (HCl) and a strong base (NaOH). It does not produce OH⁻ ions in solution and does not exhibit basic properties. Therefore, NaCl is not a base.

3. **Conclusion**:
- Based on the analysis, the substance that is **not a base** is **Option 4: NaCl**.

### Final Answer:
**NaCl (Sodium Chloride)** is not a base.

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