The fusion mixture is a mixture of

Options

A. Mixture of `Na_2CO_3 + NaHCO_3`
B. `Na_2CO_3. 10H_2O`
C. Mixture of `K_2CO_3` + `Na_2CO_3`
D. `NaHCO_3`

Explanation

To solve the question regarding what a fusion mixture is, we need to analyze the provided options and understand the concept of a fusion mixture in chemistry.

### Step-by-Step Solution:

1. **Understanding Fusion Mixture**:
- A fusion mixture in chemistry typically refers to a combination of certain salts that are heated together to form a homogeneous mixture. This is often used in qualitative analysis to test for the presence of various ions or organic compounds.

2. **Analyzing the Options**:
- **Option A**: Mixture of sodium carbonate and sodium bicarbonate.
- Sodium carbonate (Na2CO3) and sodium bicarbonate (NaHCO3) are both sodium salts, but this combination is not typically referred to as a fusion mixture.

- **Option B**: Mixture of sodium carbonate with hydrate of water.
- This option suggests a mixture involving water, which does not align with the definition of a fusion mixture.

- **Option C**: Mixture of potassium carbonate and sodium carbonate.
- This option includes two different alkali metal carbonates, which is more aligned with the concept of a fusion mixture used in qualitative analysis.

3. **Conclusion**:
- The correct answer is **Option C**: Mixture of potassium carbonate and sodium carbonate. This mixture is commonly used in fusion processes to test for various organic compounds.

### Final Answer:
The fusion mixture is a mixture of **potassium carbonate and sodium carbonate**.

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