Electrolysis is used to obtain chlorine and caustic soda from_________.

Options

A. Water
B. Copper sulphate
C. Common salt
D. Magnesium chloride

Answer

To solve the question "Electrolysis is used to obtain chlorine and caustic soda from_________", we will follow these steps:

### Step-by-Step Solution:

1. **Identify the Products**: We need to obtain chlorine (Cl₂) and caustic soda (sodium hydroxide, NaOH) through electrolysis.

2. **Review the Options**: The options provided are:
- Water (H₂O)
- Copper sulfate (CuSO₄)
- Common salt (NaCl)
- Magnesium chloride (MgCl₂)

3. **Determine the Source**: We need to find which of these substances can be electrolyzed to produce both chlorine and sodium hydroxide.

4. **Analyze Common Salt (NaCl)**:
- When NaCl is dissolved in water, it dissociates into sodium ions (Na⁺) and chloride ions (Cl⁻).
- During electrolysis, at the cathode (negative electrode), Na⁺ ions are reduced to form sodium (Na), and water (H₂O) is also present, which can provide hydroxide ions (OH⁻).
- At the anode (positive electrode), Cl⁻ ions are oxidized to form chlorine gas (Cl₂).

5. **Write the Reactions**:
- At the cathode:
\[ 2H₂O + 2e⁻ \rightarrow H₂ + 2OH⁻ \]
(This produces hydroxide ions, which combine with sodium to form NaOH.)
- At the anode:
\[ 2Cl⁻ \rightarrow Cl₂ + 2e⁻ \]
(This produces chlorine gas.)

6. **Conclusion**: The electrolysis of common salt (NaCl) in water produces both chlorine gas and sodium hydroxide. Therefore, the correct answer is **common salt (NaCl)**.

### Final Answer:
Electrolysis is used to obtain chlorine and caustic soda from **common salt (NaCl)**.

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