During the production of iron and steel.

Options

A. The oxide ore is primarily reduced to iron by solid coke according to the reaction
`2Fe_(2)O+3C to 4Fe+3CO_(2)`
B. The oxide ore is reduced by the carbon monoxide according to the reaction
`Fe_(2)O_(3)+3CO to 2Fe+3CO_(2)`
C. Major silica impurities are removed as calcium silicate slag by addition of a fluxing agent limestone
D. The silicate slag is used in manufacturing cement

Explanation

### Step-by-Step Solution:

1. **Understanding the Reduction Process**:
- The extraction of iron from its ore involves reducing iron oxide (Fe2O3) to iron (Fe). This reduction can occur through different methods, primarily using carbon monoxide (CO) or solid coke (carbon).

2. **Evaluating the First Statement**:
- The first statement claims that the oxide ore is primarily reduced to iron by solid coke. However, this is incorrect. The primary reduction occurs via carbon monoxide because it operates at a lower temperature (500 to 800 Kelvin) compared to solid coke, which requires temperatures greater than 1500 Kelvin. Therefore, this statement is **false**.

3. **Evaluating the Second Statement**:
- The second statement mentions that the oxide ore is reduced by carbon monoxide according to the reaction:
\[ \text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2 \]
- This statement is correct, as carbon monoxide effectively reduces iron oxide at the specified temperature range. Thus, this statement is **true**.

4. **Evaluating the Third Statement**:
- The third statement discusses the removal of silica impurities as calcium silicate slag by adding limestone. This is indeed correct. When limestone (CaCO3) is heated, it decomposes to CaO and CO2 at around 1000 Kelvin. The CaO then reacts with silica (SiO2) to form calcium silicate (CaSiO3), which is the slag. Therefore, this statement is **true**.

5. **Evaluating the Fourth Statement**:
- The fourth statement asserts that the silicate slag is used in manufacturing cement. This is also correct, as the calcium silicate slag produced during the iron extraction process can be utilized in cement production. Thus, this statement is **true**.

### Summary of Statements:
- **Statement 1**: Incorrect
- **Statement 2**: Correct
- **Statement 3**: Correct
- **Statement 4**: Correct

### Final Conclusion:
The correct options are **2, 3, and 4**.

---