Oxygen and hydrogen gas are produced at the anode and cathode during the electrolysis of fairly concentration aqueous solution of :

Options

A. `K_2SO_4`
B. `AgNO_3`
C. `H_2SO_4`
D. NaOH

Answer

To determine which aqueous solutions produce oxygen and hydrogen gas during electrolysis, we will analyze each option based on the ions present and their reduction/oxidation potentials.

### Step-by-Step Solution:

1. **Identify the Ions in Each Solution:**
- **K₂SO₄:** The ions present are K⁺, SO₄²⁻, H⁺, and OH⁻.
- **AgNO₃:** The ions present are Ag⁺, NO₃⁻, H⁺, and OH⁻.
- **H₂SO₄:** The ions present are H⁺, SO₄²⁻, and OH⁻.
- **NaOH:** The ions present are Na⁺ and OH⁻.

2. **Analyze K₂SO₄:**
- At the **cathode**, H⁺ ions will be reduced to form hydrogen gas (H₂):
\[ 2H^+ + 2e^- \rightarrow H_2 \]
- At the **anode**, OH⁻ ions will be oxidized to form oxygen gas (O₂):
\[ 2OH^- \rightarrow \frac{1}{2}O_2 + 2H^+ \]
- **Conclusion:** K₂SO₄ produces oxygen at the anode and hydrogen at the cathode.

3. **Analyze AgNO₃:**
- At the **cathode**, Ag⁺ ions will be reduced to form solid silver (Ag):
\[ Ag^+ + e^- \rightarrow Ag \]
- No hydrogen gas is produced at the cathode.
- **Conclusion:** AgNO₃ does not produce hydrogen gas.

4. **Analyze H₂SO₄:**
- At the **cathode**, H⁺ ions will be reduced to form hydrogen gas (H₂):
\[ 2H^+ + 2e^- \rightarrow H_2 \]
- At the **anode**, OH⁻ ions will be oxidized to form oxygen gas (O₂):
\[ 2OH^- \rightarrow \frac{1}{2}O_2 + 2H^+ \]
- **Conclusion:** H₂SO₄ produces oxygen at the anode and hydrogen at the cathode.

5. **Analyze NaOH:**
- At the **cathode**, H⁺ ions (from water) will be reduced to form hydrogen gas (H₂):
\[ 2H^+ + 2e^- \rightarrow H_2 \]
- At the **anode**, OH⁻ ions will be oxidized to form oxygen gas (O₂):
\[ 2OH^- \rightarrow \frac{1}{2}O_2 + 2H^+ \]
- **Conclusion:** NaOH produces oxygen at the anode and hydrogen at the cathode.

### Final Answer:
The solutions that produce oxygen and hydrogen gas during electrolysis are:
- K₂SO₄
- H₂SO₄
- NaOH