Questions given below are based on the given diagram for extractive metallurgy.
(iv) At `1100^@C`, which reaction is spontaneous to a maximum extent ?

Options

A. `MgO + C rarr Mg + CO`
B. `ZnO + C rarr Zn + CO`
C. `MgO + Zn rarr Mg + ZnO`
D. `ZnO + Mg rarr MgO + Zn`

Explanation

To determine which reaction is spontaneous to a maximum extent at 1100°C, we need to analyze the given reactions based on their Gibbs free energy (ΔG). A reaction is considered spontaneous if ΔG is negative.

### Step-by-Step Solution:

1. **Understand the Concept of Spontaneity**:
- A reaction is spontaneous when ΔG < 0. This indicates that the reactants can convert to products without the need for external energy.

2. **Analyze Each Reaction**:
- We will evaluate the given options one by one to see which reaction has the most negative ΔG.

3. **Option A: Magnesium Oxide and Carbon**:
- The reaction involves magnesium oxide (MgO) and carbon (C) producing carbon monoxide (CO) and magnesium (Mg).
- Here, carbon is reducing magnesium oxide. However, magnesium has a more negative ΔG than carbon, meaning magnesium can reduce carbon, not the other way around. Thus, this reaction is not spontaneous.

4. **Option B: Zinc Oxide and Carbon**:
- This reaction involves zinc oxide (ZnO) and carbon producing zinc (Zn) and carbon monoxide (CO).
- In this case, zinc is reducing carbon monoxide. However, since zinc is less reactive than carbon, this reaction is also not spontaneous.

5. **Option C: Magnesium Oxide Formation**:
- This option involves magnesium oxide (MgO) and zinc (Zn) where zinc is acting as a reducing agent.
- Since magnesium is below zinc in the reactivity series, magnesium cannot reduce zinc oxide. Therefore, this reaction is not spontaneous.

6. **Option D: Magnesium and Zinc Oxide**:
- This reaction involves magnesium (Mg) and zinc oxide (ZnO) producing zinc (Zn) and magnesium oxide (MgO).
- Here, magnesium is reducing zinc oxide to zinc. Since magnesium has a more negative ΔG compared to zinc, this reaction is spontaneous to a maximum extent.

7. **Conclusion**:
- The reaction that is spontaneous to a maximum extent at 1100°C is the one where magnesium reduces zinc oxide to zinc.

### Final Answer:
**The reaction where magnesium reduces zinc oxide to zinc (Option D) is spontaneous to a maximum extent at 1100°C.**