The correct increasing order of pH of 0.1 M solution of the following salts/acids is:

Options

A. `NaCl lt NH_4Cl lt NaCN lt HCl`
B. `HCl lt NH_4Cl lt NaCl lt NaCN`
C. `NaCN lt NH_4Cl lt NaCl lt HCl`
D. `HCl lt NaCl lt NaCN lt NH_4Cl`

Answer

To determine the correct increasing order of pH for a 0.1 M solution of the given salts and acids (NaCl, NH4Cl, NaCN, and HCl), we need to analyze each compound based on its acidic or basic nature.

### Step-by-Step Solution:

1. **Identify the Nature of Each Compound**:
- **NaCl**: This is a salt formed from a strong acid (HCl) and a strong base (NaOH). The pH of a neutral salt solution is 7.
- **NH4Cl**: This is a salt formed from a weak base (NH3) and a strong acid (HCl). It will produce H⁺ ions in solution, resulting in a pH less than 7.
- **NaCN**: This is a salt formed from a strong base (NaOH) and a weak acid (HCN). It will produce OH⁻ ions in solution, resulting in a pH greater than 7.
- **HCl**: This is a strong acid and will have a low pH, typically much less than 7.

2. **Determine the pH of Each Compound**:
- **NaCl**: pH = 7 (neutral)
- **NH4Cl**: pH < 7 (acidic)
- **NaCN**: pH > 7 (basic)
- **HCl**: pH < 7 (acidic)

3. **Order the pH Values**:
- Since HCl and NH4Cl both have pH values less than 7, we need to determine which is lower. HCl, being a strong acid, will have a lower pH than NH4Cl.
- Therefore, the order from lowest to highest pH is:
- HCl < NH4Cl < NaCl < NaCN

4. **Final Increasing Order of pH**:
- The correct increasing order of pH for the 0.1 M solutions is:
- HCl < NH4Cl < NaCl < NaCN

### Conclusion:
The correct increasing order of pH is:
**HCl < NH4Cl < NaCl < NaCN**