Which is acidic flux ?

Options

A. CaO
B. MgO
C. `SiO_2`
D. All of these

Answer

To determine which substance is an acidic flux, we will analyze the options provided.

### Step-by-Step Solution:

1. **Understanding Acidic Flux**:
- An acidic flux is a substance that can react with basic impurities during processes like metal welding or smelting. Acidic fluxes typically include compounds that can neutralize bases.

2. **Evaluating the Options**:
- **Option 1: Calcium Oxide (CaO)**:
- Calcium oxide is a basic oxide. It is not an acidic flux; rather, it can be considered a basic impurity.
- **Option 2: Magnesium Oxide (MgO)**:
- Similar to calcium oxide, magnesium oxide is also a basic oxide and thus does not qualify as an acidic flux.
- **Option 3: Silicon Dioxide (SiO2)**:
- Silicon dioxide is known to be an acidic oxide. It can react with basic impurities like CaO and MgO, making it an acidic flux.
- **Option 4: All of these**:
- Since only SiO2 is an acidic flux, this option is incorrect.

3. **Conclusion**:
- After evaluating all the options, the correct answer is **Option 3: SiO2**. It is the only substance among the options that acts as an acidic flux.

### Final Answer:
The acidic flux is **SiO2**.

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