The correct statement is

Options

A. leaching of bauxite using concentrated `NaOH` solution gives sodium aluminate and sodium silicate
B. the blistered apperance of copper during the metallurgical process is due to the evoluation of `CO_(2)`
C. pig iron is obtained from cast iron
D. the Hall - Heroult process is used for the production of aluminium and iron

Answer

To solve the question regarding the correct statement about the extraction of aluminum and related processes, we will analyze the information provided in the video transcript step by step.

### Step 1: Understanding the Leaching Process of Bauxite
- Bauxite, the principal ore of aluminum, undergoes a leaching process using concentrated sodium hydroxide (NaOH).
- During this process, sodium aluminate (NaAlO2) and sodium silicate (Na2SiO3) are formed, while impurities such as iron(III) oxide (Fe2O3) precipitate out.

**Hint:** Focus on the chemical reactions involved in the leaching of bauxite and the products formed.

### Step 2: Identifying the Impurities and Their Reactions
- The impurities in bauxite include Fe2O3 and SiO2.
- Fe2O3 precipitates out during the leaching process, while SiO2 reacts with NaOH to form soluble sodium silicate.

**Hint:** Remember the role of impurities in the extraction process and how they interact with the reagents.

### Step 3: Understanding the Bayer's Process
- The leaching of bauxite is part of the Bayer's process, which is the primary method for extracting aluminum from its ore.
- The overall reaction involves the formation of sodium aluminate and the subsequent precipitation of aluminum hydroxide (Al(OH)3) when water is added.

**Hint:** Bayer's process is crucial for aluminum extraction; knowing its steps will help in identifying the correct statement.

### Step 4: Analyzing the Blistered Appearance of Copper
- The transcript mentions that the blistered appearance of copper during metallurgy is due to the evolution of sulfur dioxide (SO2) gas, not carbon dioxide (CO2).
- This occurs during the self-reduction of copper(I) sulfide (Cu2S) in the presence of copper(II) oxide (Cu2O).

**Hint:** Pay attention to the gases evolved during metallurgical processes and their effects on the materials.

### Step 5: Evaluating the Statements
- The first statement regarding the leaching of bauxite and the formation of sodium aluminate and sodium silicate is correct.
- The second statement about the blistered appearance of copper due to SO2 is also correct.
- The third and fourth statements regarding impurities in cast iron and pig iron, and the Hall-Héroult process for aluminum extraction, need to be evaluated based on their accuracy.

**Hint:** Cross-check each statement against the information provided in the transcript.

### Conclusion
After evaluating all the statements based on the information from the transcript, the correct statement is identified. The first statement regarding the leaching of bauxite is confirmed to be accurate.

### Final Answer
The correct statement is the first one regarding the leaching of bauxite using concentrated NaOH to produce sodium aluminate and sodium silicate.