Which of the following statements is incorrect ?

Options

A. In Hall`-` Heroult process, the electrolyte used is a molten mixture of alumina, sodium hydroxide and cryolite
B. Lead is extracted from its chief ore by both carbon reduction and self reduction.
C. Zinc is extracted from its chief ore by carbon reduction.
D. Extraction of gold involves the leaching of ore with cyanide solution followed by reduction with zinc.

Explanation

To determine which statement is incorrect regarding metallurgy, we will analyze each statement one by one.

### Step 1: Analyze the First Statement
**Statement:** In Hall-Heroult's process, the electrolyte used is a molten mixture of alumina, sodium hydroxide, and cryolite.

**Analysis:**
- The Hall-Heroult process is used for the extraction of aluminum.
- The correct electrolyte used in this process is a molten mixture of alumina (Al₂O₃) and cryolite (Na₃AlF₆).
- Sodium hydroxide (NaOH) is **not** used in this process.

**Conclusion:** This statement is incorrect.

### Step 2: Analyze the Second Statement
**Statement:** Lead is extracted from its chief ore by both carbon reduction and self-reduction.

**Analysis:**
- The chief ore of lead is galena (PbS).
- During the extraction process, PbS is roasted to form PbO and SO₂.
- PbO can be reduced by carbon (carbon reduction) and also can reduce PbS (self-reduction).

**Conclusion:** This statement is correct.

### Step 3: Analyze the Third Statement
**Statement:** Zinc is extracted from its chief ore by carbon reduction.

**Analysis:**
- The chief ore of zinc is sphalerite (ZnS).
- ZnS is roasted to form ZnO.
- ZnO is then reduced by carbon to produce zinc.

**Conclusion:** This statement is correct.

### Step 4: Analyze the Fourth Statement
**Statement:** The extraction of gold involves the leaching of ore with cyanide solution followed by reduction with zinc.

**Analysis:**
- Gold is extracted using the cyanide process, where the ore is leached with a cyanide solution to form a complex ion.
- Zinc is then used to reduce this complex ion to recover gold.

**Conclusion:** This statement is correct.

### Final Conclusion
After analyzing all statements, we find that:
- The **first statement** is incorrect.
- The **second, third, and fourth statements** are correct.

Thus, the answer to the question is that the first statement is incorrect.

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