Which solution will have the lowest pH value ?

Options

A. 0.10 M HCN
B. `0.10 M HNO_3`
C. `0.10 M NaCl`
D. `0.10 "M "H_2CO_3`

Answer

To determine which solution will have the lowest pH value among the given options, we can follow these steps:

### Step 1: Identify the Solutions
We have four solutions to consider:
1. 0.1 M solution of SCN (thiocyanate ion)
2. 0.1 M solution of nitric acid (HNO3)
3. 0.1 M solution of sodium chloride (NaCl)
4. 0.1 M solution of carbonic acid (H2CO3)

### Step 2: Understand pH and Acidity
pH is a measure of the acidity or basicity of a solution. The lower the pH, the more acidic the solution is. Strong acids will have lower pH values compared to weak acids or neutral solutions.

### Step 3: Analyze Each Solution
- **SCN (Thiocyanate ion)**: This is a weak acid, so it will have a higher pH compared to strong acids.
- **HNO3 (Nitric acid)**: This is a strong acid, which completely dissociates in solution, resulting in a low pH.
- **NaCl (Sodium chloride)**: This is a neutral salt formed from a strong acid (HCl) and a strong base (NaOH). Its pH is approximately 7.
- **H2CO3 (Carbonic acid)**: This is a weak acid and will have a higher pH than strong acids like HNO3.

### Step 4: Compare the Acidity
From the analysis:
- HNO3 is the strongest acid among the four solutions, meaning it will have the lowest pH.
- SCN and H2CO3 are weak acids, resulting in higher pH values.
- NaCl is neutral, with a pH around 7.

### Step 5: Conclusion
Since HNO3 is the strongest acid, the 0.1 M solution of nitric acid will have the lowest pH value compared to the other solutions.

### Final Answer
The solution with the lowest pH value is the **0.1 M solution of nitric acid (HNO3)**.

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