Electrolysis of aqueous sodium chloride solution will form ______ at the cathode.A. Hydrogen gas B. Sodium metalC. WaterD. Chlorine gas

The correct answer is A. Hydrogen gas.

Here's a detailed explanation of the electrolysis of aqueous sodium chloride (NaCl) solution:

1. **Process of Electrolysis**: Electrolysis is a process that uses electrical energy to drive a chemical reaction. In the case of aqueous sodium chloride, when an electric current is passed through the solution, it breaks down into its constituent ions.

2. **Ions Present**: In an aqueous solution of sodium chloride, the following ions are present:
- Sodium ions (Na⁺)
- Chloride ions (Cl⁻)
- Water molecules (H₂O) which dissociate into hydrogen ions (H⁺) and hydroxide ions (OH⁻).

3. **Electrode Reactions**:
- At the **cathode** (the negative electrode), reduction occurs. The available species that can gain electrons are the sodium ions (Na⁺) and the hydrogen ions (H⁺) from the dissociation of water.
- If Na⁺ were to be reduced, it would form sodium metal, but sodium metal is highly reactive and not stable in water, leading to further reactions.
- Therefore, H⁺ ions are preferentially reduced to form hydrogen gas (H₂) according to the half-reaction:
\[ 2H^+ + 2e^- \rightarrow H_2(g) \]

- At the **anode** (the positive electrode), oxidation occurs. Chloride ions (Cl⁻) are oxidized to form chlorine gas (Cl₂) according to the half-reaction:
\[ 2Cl^- \rightarrow Cl_2(g) + 2e^- \]

4. **Conclusion**: Thus, during the electrolysis of aqueous sodium chloride, hydrogen gas is produced at the cathode, making the correct answer A. Hydrogen gas.

In summary, the electrolysis of aqueous sodium chloride solution produces hydrogen gas at the cathode and chlorine gas at the anode.