How mant reaction can show slag formation process from the given reaction ?
(i) `SiO_(2) + CaO rarr CaSiO_(3)`
(ii) `FeO + SiO_(2) rarr FeSiO_(3)`
(iii) `CaO + P_(2)O_(5) rarr Ca_(3)(PO_(4))_(2)`
(iv) `Cr_(2)O_(3) + 2Al rarr Al_(2)O_(3) + 2Cr`
(v) `MgCO_(3) + SiO_(2) rarr MgSiO_(3) + CO_(2)`.

Explanation

To determine how many reactions show the slag formation process from the given reactions, we need to analyze each reaction step by step.

### Step-by-Step Solution:

1. **Identify the definition of slag**:
- Slag is a glass-like by-product formed during the extraction of metals, typically resulting from the reaction of acidic and basic fluxes.

2. **Analyze the first reaction**:
- Reaction: `SiO₂ + CaO → CaSiO₃`
- Here, silicon dioxide (SiO₂) acts as the acidic flux and calcium oxide (CaO) acts as the basic flux. The product, calcium silicate (CaSiO₃), is a slag.
- **Conclusion**: This reaction shows slag formation.

3. **Analyze the second reaction**:
- Reaction: `FeO + SiO₂ → FeSiO₃`
- Iron oxide (FeO) is the basic flux and silicon dioxide (SiO₂) is the acidic flux. The product, iron silicate (FeSiO₃), is also a slag.
- **Conclusion**: This reaction shows slag formation.

4. **Analyze the third reaction**:
- Reaction: `CaO + P₂O₅ → Ca₃(PO₄)₂`
- Calcium oxide (CaO) is the basic flux and phosphorus pentoxide (P₂O₅) is the acidic flux. The product, calcium phosphate (Ca₃(PO₄)₂), can be considered a type of slag.
- **Conclusion**: This reaction shows slag formation.

5. **Analyze the fourth reaction**:
- Reaction: `Cr₂O₃ + 2Al → Al₂O₃ + 2Cr`
- In this reaction, chromium oxide (Cr₂O₃) reacts with aluminum (Al) to produce aluminum oxide (Al₂O₃) and chromium (Cr). The aluminum oxide can be considered a by-product, which can be classified as slag.
- **Conclusion**: This reaction shows slag formation.

6. **Analyze the fifth reaction**:
- Reaction: `MgCO₃ + SiO₂ → MgSiO₃ + CO₂`
- Here, magnesium carbonate (MgCO₃) reacts with silicon dioxide (SiO₂) to produce magnesium silicate (MgSiO₃) and carbon dioxide (CO₂). However, since there is no separation of a metal from impurities, this does not qualify as slag formation.
- **Conclusion**: This reaction does not show slag formation.

### Final Conclusion:
- The reactions that show slag formation are:
1. `SiO₂ + CaO → CaSiO₃`
2. `FeO + SiO₂ → FeSiO₃`
3. `CaO + P₂O₅ → Ca₃(PO₄)₂`
4. `Cr₂O₃ + 2Al → Al₂O₃ + 2Cr`

- Therefore, **4 reactions** show the slag formation process.