The set having incorrect statement is
1. the Hall-Heroult process is used for the production of aluminum and iron
2. pig iron is obtained from cast iron.
3. the blistered appearance of copper during the metallurgical process is due to the evolution of `CO_2`
4. leaching of bauxite using concentrated NaOH solution gives sodium aluminate and sodium silicate

Options

A. 1,2
B. 2,3
C. 1,2,3
D. 1,2,4

Answer

To solve the question regarding the incorrect statements, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement 1: The Hall-Heroult process is used for the production of aluminum and iron.**
- The Hall-Heroult process is specifically used for the production of aluminum from bauxite. It does not produce iron. Therefore, this statement is **incorrect**.

2. **Statement 2: Pig iron is obtained from cast iron.**
- This statement is also incorrect. Pig iron is actually the raw iron produced from iron ore in a blast furnace and is used to make cast iron. Cast iron is produced by melting pig iron with scrap iron and other alloying elements. Thus, this statement is **incorrect**.

3. **Statement 3: The blistered appearance of copper during the metallurgical process is due to the evolution of CO2.**
- The blistered appearance of copper is actually due to the evolution of sulfur dioxide (SO2) during the smelting of copper ores, not carbon dioxide (CO2). Therefore, this statement is **incorrect**.

4. **Statement 4: Leaching of bauxite using concentrated NaOH solution gives sodium aluminate and sodium silicate.**
- This statement is correct. When bauxite is treated with concentrated NaOH, sodium aluminate and sodium silicate are formed. The aluminum oxide (Al2O3) reacts with NaOH to form soluble sodium aluminate, and silica (SiO2) reacts to form sodium silicate. Thus, this statement is **correct**.

### Conclusion:
The incorrect statements are 1, 2, and 3. Therefore, the set having incorrect statements is option 3.

### Final Answer:
The set having incorrect statements is **1, 2, and 3**.

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