The electrolysis of a solution resulted in the formation of `H_2`(g) at the cathode and `Cl_(2)` (g) at anode. The solution is :

Options

A. water
B. `H_2SO_4(aq)`
C. highly concentrated NaCl(aq) solution
D. `CuCl_2(aq)`

Answer

To determine the solution that results in the formation of hydrogen gas (H₂) at the cathode and chlorine gas (Cl₂) at the anode during electrolysis, we can follow these steps:

### Step 1: Understand the Electrolysis Process
Electrolysis involves the breakdown of an ionic compound in solution by passing an electric current through it. The process occurs in two parts:
- **At the Cathode (Reduction)**: Cations gain electrons to form neutral atoms or molecules.
- **At the Anode (Oxidation)**: Anions lose electrons to form neutral atoms or molecules.

### Step 2: Identify the Reactions at the Electrodes
- **At the Cathode**: The formation of H₂ gas indicates that H⁺ ions are being reduced. The half-reaction can be written as:
\[ 2H^+ + 2e^- \rightarrow H_2(g) \]

- **At the Anode**: The formation of Cl₂ gas indicates that Cl⁻ ions are being oxidized. The half-reaction can be written as:
\[ 2Cl^- \rightarrow Cl_2(g) + 2e^- \]

### Step 3: Determine the Required Ions in the Solution
To produce H₂ and Cl₂, the solution must contain:
- **H⁺ ions**: These can come from water or an acid.
- **Cl⁻ ions**: These must come from a salt like NaCl or KCl.

### Step 4: Analyze the Given Options
1. **Water**: Contains H⁺ ions but no Cl⁻ ions. **(Incorrect)**
2. **H₂SO₄**: Contains H⁺ ions but no Cl⁻ ions. **(Incorrect)**
3. **Highly Concentrated NaCl Solution**: Contains Na⁺ and Cl⁻ ions. When dissolved, it also provides H⁺ ions from water. This solution can produce H₂ at the cathode and Cl₂ at the anode. **(Correct)**
4. **CuCl₂ Solution**: Contains Cu²⁺ and Cl⁻ ions. While Cl⁻ can produce Cl₂, the Cu²⁺ would preferentially be reduced to Cu instead of producing H₂. **(Incorrect)**

### Step 5: Conclusion
The solution that results in the formation of H₂ gas at the cathode and Cl₂ gas at the anode is **highly concentrated NaCl aqueous solution**.

### Final Answer
The correct solution is **highly concentrated NaCl aqueous solution**.

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