If Pt is used as cathode in the electrolysis of aqueous NaCl solution, the ion reduced at cathode is :

Options

A. `H^+`
B. `Na^+`
C. `OH^-`
D. `Cl^-`

Answer

To determine which ion is reduced at the cathode during the electrolysis of an aqueous NaCl solution using platinum as the cathode, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Components in Aqueous NaCl Solution**:
- When NaCl is dissolved in water, it dissociates into sodium ions (Na⁺) and chloride ions (Cl⁻).
- Additionally, water (H₂O) dissociates into hydrogen ions (H⁺) and hydroxide ions (OH⁻).
- Therefore, the ions present in the solution are Na⁺, Cl⁻, H⁺, and OH⁻.

2. **Understand the Electrolysis Process**:
- During electrolysis, oxidation occurs at the anode and reduction occurs at the cathode.
- At the cathode, we need to determine which ions can be reduced (gain electrons).

3. **Identify Possible Reducing Agents at the Cathode**:
- The possible ions that can be reduced at the cathode are Na⁺ and H⁺.
- The reduction reactions are as follows:
- For Na⁺:
\[ \text{Na}^+ + e^- \rightarrow \text{Na} \quad (\text{E}^\circ = -2.71 \, \text{V}) \]
- For H⁺:
\[ \text{H}^+ + e^- \rightarrow \text{H}_2 \quad (\text{E}^\circ = 0 \, \text{V}) \]

4. **Compare the Standard Reduction Potentials**:
- The standard reduction potential for H⁺ is 0 V, which is more positive than the standard reduction potential for Na⁺ (-2.71 V).
- Since reduction occurs at the cathode, the species with the more positive reduction potential will be reduced preferentially.

5. **Determine the Ion Reduced at the Cathode**:
- Since H⁺ has a higher (more positive) reduction potential than Na⁺, H⁺ will be reduced to form hydrogen gas (H₂).
- Therefore, the ion that is reduced at the cathode is H⁺.

### Final Answer:
The ion reduced at the cathode is **H⁺**.

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