The pair that requires calcination is

Options

A. `ZnCO_3 and CaO`
B. `Fe_2O_3 .xH_2Oand CaCO_3.MgCO_3`
C. `ZnO and Fe_2O_3.xH_2O`
D. All of these

Answer

To determine the pair that requires calcination, we first need to understand what calcination is and the types of compounds that typically undergo this process.

### Step 1: Understanding Calcination
Calcination is a thermal treatment process in which ores or other solid materials are heated to a high temperature in the absence of air or in a controlled atmosphere. The main purpose of calcination is to remove volatile substances (like water or carbon dioxide) and to convert metal carbonates into metal oxides.

### Step 2: Analyzing the Options
We have four options to analyze:

- **Option A:** Zinc Carbonate and Calcium Oxide
- **Option B:** Fe2O3 and Calcium Carbonate
- **Option C:** Zinc Oxide and Fe2O3.XH2O
- **Option D:** All of the above

### Step 3: Identifying Compounds Requiring Calcination
1. **Zinc Carbonate (ZnCO3)**: This compound can undergo calcination to form Zinc Oxide (ZnO) and release carbon dioxide (CO2).

2. **Calcium Oxide (CaO)**: This is already an oxide and does not require calcination.

3. **Fe2O3 (Iron(III) oxide)**: This is already an oxide and does not require calcination.

4. **Calcium Carbonate (CaCO3)**: This compound can undergo calcination to form Calcium Oxide (CaO) and release carbon dioxide (CO2).

5. **Zinc Oxide (ZnO)**: This is already an oxide and does not require calcination.

6. **Fe2O3.XH2O (Hydrated Iron(III) oxide)**: This hydrated compound can undergo calcination to remove water and convert to Fe2O3.

### Step 4: Conclusion
From the analysis:
- Zinc Carbonate requires calcination.
- Calcium Carbonate requires calcination.
- Hydrated Iron(III) oxide requires calcination.

Thus, the pairs that require calcination are:
- Zinc Carbonate
- Calcium Carbonate
- Hydrated Iron(III) oxide

Since both options A and B contain compounds that require calcination, and option C also includes a hydrated oxide that requires calcination, we conclude that:

**The correct answer is Option D: All of the above.**