Which of the following aqueous solution will have a `pH` less than `7.0 ?

Options

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

Answer

To determine which of the following aqueous solutions will have a pH less than 7.0, we need to analyze the nature of the salts provided and their hydrolysis reactions. A solution will have a pH less than 7 if it is acidic, which typically occurs when a salt is formed from a strong acid and a weak base.

### Step-by-Step Solution:

1. **Identify the Salts**: We need to consider the salts provided in the options. Let's assume the options are:
- A) KNO3
- B) NaOH
- C) FeCl3
- D) NaCN

2. **Analyze Each Salt**:
- **A) KNO3**:
- KNO3 is formed from KOH (a strong base) and HNO3 (a strong acid).
- Hydrolysis: KNO3 → K⁺ + NO3⁻ (no acidic or basic properties).
- Result: Neutral solution (pH = 7).

- **B) NaOH**:
- NaOH is a strong base.
- Result: Basic solution (pH > 7).

- **C) FeCl3**:
- FeCl3 is formed from Fe(OH)3 (a weak base) and HCl (a strong acid).
- Hydrolysis: FeCl3 + 3H2O → Fe(OH)3 + 3H⁺ + 3Cl⁻.
- Result: Acidic solution (pH < 7).

- **D) NaCN**:
- NaCN is formed from NaOH (a strong base) and HCN (a weak acid).
- Hydrolysis: NaCN → Na⁺ + CN⁻ (CN⁻ can react with water to form OH⁻).
- Result: Basic solution (pH > 7).

3. **Conclusion**:
- Among the given options, only **FeCl3** will produce an acidic solution with a pH less than 7.
- Therefore, the correct answer is **C) FeCl3**.