Electrolysis is an important technique for extraction of metals, and each ion of the solution needs a minimum voltage to get discharged and this value is expressed in terms of discharge potential. For some metal ions the discharge potentials follow the order given below :
`Li^(+) gt K^(+) gt Ca^(2+) gt Na^(+) gt Mg^(2+) gt Al^(3+) gt Zn^(2+) gt Fe^(2+) gt Ni^(2+) gt H_(3)O^(+) gt Cu^(2+) gt Hg_(2)^(2+) gt Ag^(+) gt Au^(3+)`
For some anions the discharge potentials are in the order :
`SO_(4)^(2-) gt NO_(3)^(-) gt OH^(-) gt Br^(-) gt I^(-)`
A mixture containing chlorides of sodium, calcium and zinc is electrolysed in presence f wate. The product obtained at cathode will be :

Options

A. Na
B. `H_(2)`
C. `Ca`
D. `Cl_(2)`

Answer

To solve the problem, we need to analyze the electrolysis of a mixture containing chlorides of sodium (NaCl), calcium (CaCl₂), and zinc (ZnCl₂) in the presence of water. We will determine which product is obtained at the cathode during the electrolysis process.

### Step-by-Step Solution:

1. **Identify the Ions Present**:
- The mixture contains Na⁺ (from NaCl), Ca²⁺ (from CaCl₂), and Zn²⁺ (from ZnCl₂). Additionally, water contributes H₃O⁺ ions (or H⁺ ions) to the solution.

2. **Understand Discharge Potentials**:
- The discharge potentials for the cations are as follows:
- Na⁺ > H₃O⁺ (Hydronium ion)
- Ca²⁺ > H₃O⁺
- Zn²⁺ > H₃O⁺
- This means that Na⁺, Ca²⁺, and Zn²⁺ have higher discharge potentials than H₃O⁺, indicating that they will not get discharged at the cathode before H₃O⁺ does.

3. **Determine the Product at the Cathode**:
- During electrolysis, the cathode is the negatively charged electrode where reduction occurs. The species that gets discharged at the cathode is the one with the lowest discharge potential.
- Since H₃O⁺ has a lower discharge potential than Na⁺, Ca²⁺, and Zn²⁺, it will be preferentially discharged.

4. **Reaction at the Cathode**:
- The discharge of H₃O⁺ ions at the cathode leads to the formation of hydrogen gas (H₂) according to the reaction:
\[ 2H_3O^+ + 2e^- \rightarrow H_2(g) + 2H_2O \]

5. **Conclusion**:
- Therefore, the product obtained at the cathode during the electrolysis of the mixture is hydrogen gas (H₂).

### Final Answer:
The product obtained at the cathode will be **hydrogen gas (H₂)**.

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