Which of the following salt on heating with concentrated `H_(2)SO_(4)`, coloured vapours do not evolve?

Options

A. `NaBr`
B. `NaNO_(3)`
C. `CaF_(2)`
D. `KI`

Explanation

To determine which salt does not evolve colored vapors when heated with concentrated sulfuric acid (H₂SO₄), we will analyze the reactions of each given salt with concentrated H₂SO₄.

### Step-by-Step Solution:

1. **Identify the salts**: The salts given are:
- Sodium bromide (NaBr)
- Sodium nitrate (NaNO₃)
- Calcium fluoride (CaF₂)
- Potassium iodide (KI)

2. **Reaction of Sodium Bromide (NaBr)**:
- When NaBr is heated with concentrated H₂SO₄, it forms sodium sulfate (Na₂SO₄) and hydrogen bromide (HBr).
- The HBr can further react with concentrated H₂SO₄ to produce bromine gas (Br₂), which is reddish-brown in color.
- **Conclusion**: Colored vapors (Br₂) evolve.

3. **Reaction of Sodium Nitrate (NaNO₃)**:
- When NaNO₃ is heated with concentrated H₂SO₄, it produces sodium sulfate (Na₂SO₄) and nitrogen dioxide (NO₂).
- NO₂ is a reddish-brown gas.
- **Conclusion**: Colored vapors (NO₂) evolve.

4. **Reaction of Calcium Fluoride (CaF₂)**:
- When CaF₂ is heated with concentrated H₂SO₄, it forms calcium sulfate (CaSO₄) and hydrogen fluoride (HF).
- HF is a colorless gas.
- **Conclusion**: No colored vapors evolve.

5. **Reaction of Potassium Iodide (KI)**:
- When KI is heated with concentrated H₂SO₄, it forms potassium sulfate (K₂SO₄) and hydrogen iodide (HI).
- HI can further react with concentrated H₂SO₄ to produce iodine (I₂), which is yellow in color.
- **Conclusion**: Colored vapors (I₂) evolve.

6. **Final Conclusion**:
- Among the salts, only calcium fluoride (CaF₂) does not evolve colored vapors when heated with concentrated sulfuric acid.

### Answer:
**Calcium fluoride (CaF₂)** is the salt that does not evolve colored vapors upon heating with concentrated H₂SO₄.