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/acids (NaCl, NH4Cl, NaCN, and HCl), we need to analyze each substance based on its acid-base properties:

### Step 1: Analyze NaCl
- **Nature**: NaCl is formed from a strong acid (HCl) and a strong base (NaOH).
- **pH**: The solution of NaCl is neutral, so the pH is approximately 7.

### Step 2: Analyze NH4Cl
- **Nature**: NH4Cl is formed from a strong acid (HCl) and a weak base (NH3).
- **pH**: The presence of NH4+ ions (from NH4Cl) will lead to the formation of H+ ions in solution, making it acidic. Therefore, the pH will be less than 7.

### Step 3: Analyze NaCN
- **Nature**: NaCN is formed from a strong base (NaOH) and a weak acid (HCN).
- **pH**: The presence of CN- ions (from NaCN) will lead to the formation of OH- ions in solution, making it basic. Therefore, the pH will be greater than 7.

### Step 4: Analyze HCl
- **Nature**: HCl is a strong acid.
- **pH**: The pH of a 0.1 M HCl solution will be very low (approximately 1), as it completely dissociates in water to give H+ ions.

### Step 5: Order the pH values
- From the analysis:
- HCl has the lowest pH (most acidic).
- NH4Cl has a pH less than 7 (acidic).
- NaCl has a pH of approximately 7 (neutral).
- NaCN has a pH greater than 7 (basic).

### Final Increasing Order of pH
- The increasing order of pH for the 0.1 M solutions is:
1. HCl (lowest pH)
2. NH4Cl
3. NaCl
4. NaCN (highest pH)

Thus, the correct increasing order of pH is:
**HCl < NH4Cl < NaCl < NaCN**