Select the incorrect statement:

Options

A. pH of 500 ml 0.001 N `HNO_(3)` is 3.0
B. pH of 500 ml 0.001 N `HNO_(3)` is 4 - log 5
C. pH of 20 ml decinormal HCI solution is 1.0
D. pH of 100 ml 0.01 N NaCI solution is = 7.0

Answer

To solve the question of selecting the incorrect statement regarding pH values, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding pH Calculation**:
- The pH of a solution is calculated using the formula:
\[ \text{pH} = -\log[\text{H}^+] \]
- For strong acids like HNO3, the concentration of H⁺ ions is equal to the concentration of the acid.

2. **Analyzing Option 1**:
- **Statement**: "pH of 500 ml 0.001 normal HNO3 is 3."
- **Calculation**:
- Normality (N) = Molarity (M) for strong acids.
- Given: 0.001 N HNO3 in 500 ml.
- Moles of HNO3 = Normality × Volume (in liters) = 0.001 × 0.5 = 0.0005 moles.
- Concentration of H⁺ = 0.0005 moles / 0.5 L = 0.001 M = 10⁻³ M.
- pH = -log(10⁻³) = 3.
- **Conclusion**: This statement is **correct**.

3. **Analyzing Option 2**:
- **Statement**: "pH of 500 ml of 0.001 normal HNO3 is 4.4 - log 5."
- **Calculation**:
- From Option 1, we already calculated that the pH is 3.
- The expression "4.4 - log 5" needs to be evaluated:
- log 5 ≈ 0.699.
- Therefore, 4.4 - log 5 ≈ 4.4 - 0.699 = 3.701.
- **Conclusion**: This statement is **incorrect** because the pH should be 3, not approximately 3.701.

4. **Analyzing Option 3**:
- **Statement**: "pH of 20 ml desi normal HCl solution is 1."
- **Assumption**: Assuming "desi normal" refers to a 1 N solution.
- **Calculation**:
- For 1 N HCl, the concentration of H⁺ = 1 M.
- pH = -log(1) = 0.
- **Conclusion**: This statement is **incorrect** if we assume 1 N, but the context might imply a different concentration. However, if it is indeed 1 N, then the pH cannot be 1.

5. **Analyzing Option 4**:
- **Statement**: "pH of 100 ml 0.01 normal NaCl is 7."
- **Conclusion**: NaCl is a neutral salt formed from a strong acid (HCl) and a strong base (NaOH), so the pH of a NaCl solution is indeed 7. This statement is **correct**.

### Final Conclusion:
The incorrect statement among the options is **Option 2**.