consider the following statements:
When a direct current is passed through an aqueous concentrated soluton of NaCl.
1. pH of the solution decreases.
2. metallic sodium will be deposited at the cathode.
3. Chlorie gas will be liberated at th anode.
4. pH of the solution increases.
Which of the statements given above are correct?

Options

A. 1 and 2
B. 2 and 3
C. 3 and 4
D. 1 and 3

Explanation

To solve the question regarding the electrolysis of an aqueous concentrated solution of NaCl, we will analyze each statement step by step.

### Step 1: Understanding the Electrolysis Process
When a direct current is passed through an aqueous concentrated solution of NaCl, electrolysis occurs. This involves the movement of ions towards the electrodes where oxidation and reduction reactions take place.

### Step 2: Identify the Reactions at the Electrodes
1. **At the Cathode (Reduction Reaction)**:
- The cathode is where reduction occurs. In this case, we have two possible species for reduction: \( \text{Na}^+ \) ions and water (\( \text{H}_2\text{O} \)).
- The reduction potential of \( \text{Na}^+ \) is lower than that of water. Therefore, water is reduced:
\[ 2 \text{H}_2\text{O} + 2e^- \rightarrow \text{H}_2(g) + 2 \text{OH}^-(aq) \]
- This reaction produces hydrogen gas and hydroxide ions, which will increase the pH of the solution.

2. **At the Anode (Oxidation Reaction)**:
- The anode is where oxidation occurs. The possible species for oxidation are \( \text{Cl}^- \) ions and water.
- Chloride ions have a higher oxidation potential compared to water, so \( \text{Cl}^- \) will be oxidized:
\[ 2 \text{Cl}^-(aq) \rightarrow \text{Cl}_2(g) + 2e^- \]
- This reaction produces chlorine gas.

### Step 3: Analyzing Each Statement
1. **Statement 1: pH of the solution decreases.**
- This statement is **incorrect**. The production of \( \text{OH}^- \) ions at the cathode increases the pH.

2. **Statement 2: Metallic sodium will be deposited at the cathode.**
- This statement is **incorrect**. Instead of metallic sodium, hydrogen gas is produced at the cathode.

3. **Statement 3: Chlorine gas will be liberated at the anode.**
- This statement is **correct**. Chlorine gas is indeed produced at the anode.

4. **Statement 4: pH of the solution increases.**
- This statement is **correct**. The generation of hydroxide ions increases the pH.

### Conclusion
The correct statements are:
- Statement 3: Chlorine gas will be liberated at the anode.
- Statement 4: pH of the solution increases.

### Final Answer
The correct statements are **3 and 4**.

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