The pH is less than 7, of the solution of

Options

A. `FeCl_(3)`
B. NaCN
C. NaOH
D. NaCl

Explanation

To determine which solution has a pH less than 7, we need to analyze the nature of each compound provided in the options.

### Step-by-Step Solution:

1. **Understanding pH and Acidity**:
- pH is a measure of the hydrogen ion concentration in a solution. A pH less than 7 indicates an acidic solution.

2. **Analyzing Each Option**:
- **Option 1: NaCl**
- NaCl is composed of Na⁺ (from NaOH, a strong base) and Cl⁻ (from HCl, a strong acid). Since both ions come from strong acid and strong base, NaCl is neutral, and its pH = 7.

- **Option 2: NaOH**
- NaOH is a strong base. Solutions of strong bases have a pH greater than 7. Therefore, NaOH cannot be the answer.

- **Option 3: NaCN**
- NaCN consists of Na⁺ (from NaOH, a strong base) and CN⁻ (from HCN, a weak acid). The presence of the weak acid CN⁻ means that the solution will be basic, resulting in a pH greater than 7.

- **Option 4: FeCl₃**
- FeCl₃ is made up of Fe³⁺ (which can hydrolyze in water to form acidic solutions) and Cl⁻ (from HCl, a strong acid). The Fe³⁺ ion will create an acidic environment in solution, leading to a pH less than 7.

3. **Conclusion**:
- After analyzing all the options, we find that the only solution that results in a pH less than 7 is **FeCl₃**. Therefore, the correct answer is **FeCl₃**.

### Final Answer:
The solution with a pH less than 7 is **FeCl₃**.