Choose the reaction which does not indicate slag formation?

Options

A. `3MgO+P_(2) O_(5) to Mg_(3)(PO_(4))_(2)`
B. `SiO_(2)+PbO to PbSio_(3)`
C. `Fe_(2)O_(3)+P_(2)O_(5) to FePO_(4) `
D. None of these

Answer

To solve the question, we need to analyze the reactions provided and determine which one does not indicate slag formation. Slag is typically formed during the extraction of metals from their ores, and it usually consists of silicates or other compounds formed by the reaction of metal oxides with impurities.

### Step-by-Step Solution:

1. **Identify the Reactions**: We are given three reactions involving different metal oxides and phosphorus pentoxide (P2O5) or lead oxide (PbO). We need to evaluate each reaction to see if it results in the formation of a slag.

2. **Reaction 1**:
- **MgO + P2O5 → Mg3(PO4)2**
- This reaction forms magnesium phosphate, which is a type of slag. Thus, this indicates slag formation.

3. **Reaction 2**:
- **SiO2 + PbO → PbSiO3**
- This reaction produces lead silicate (PbSiO3), which is also considered a slag. Hence, this indicates slag formation.

4. **Reaction 3**:
- **Fe2O3 + P2O5 → FePO4**
- This reaction results in iron phosphate (FePO4), which can also be classified as a slag. Therefore, this indicates slag formation.

5. **Conclusion**:
- All three reactions indicate slag formation. The question asks for the reaction that does not indicate slag formation. Since all three provided reactions form slag, the correct answer is option 4: "None of these."

### Final Answer:
**The reaction which does not indicate slag formation is option 4: None of these.**