Which of the following statements is/are correct?
I. The flame of a Bunsen burner is blue when the air hole is open and yellow when the air hole is closed.
II. The liquid or solid wax never catches fire.
III. A substance cannot catch fire if its temperature is higher than its ignition temperature.
IV. Water should be poured over burning petrol, kerosene or diesel.
V. The middle zone of a candle emits the least light

Options

A. I and II only
B. III and IV only
C. II,III and IV only
D. V only

Explanation

To determine which statements are correct, let's analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement I: The flame of a Bunsen burner is blue when the air hole is open and yellow when the air hole is closed.**
- **Analysis:** When the air hole of a Bunsen burner is open, there is a complete combustion due to the excess supply of air, resulting in a blue flame. Conversely, when the air hole is closed, there is limited air supply, leading to partial combustion and a yellow flame.
- **Conclusion:** This statement is **correct**.

2. **Statement II: The liquid or solid wax never catches fire.**
- **Analysis:** While the wax itself does not catch fire, the wick (thread) within the wax does catch fire. The statement implies that wax cannot burn at all, which is misleading.
- **Conclusion:** This statement is **incorrect**.

3. **Statement III: A substance cannot catch fire if its temperature is higher than its ignition temperature.**
- **Analysis:** Ignition temperature is the minimum temperature at which a substance starts to burn. If the temperature of a substance is higher than its ignition temperature, it can easily catch fire.
- **Conclusion:** This statement is **incorrect**.

4. **Statement IV: Water should be poured over burning petrol, kerosene or diesel.**
- **Analysis:** Water is heavier than petrol, kerosene, and diesel, and when poured on these burning substances, it sinks and does not extinguish the fire effectively. Instead, the fire continues to burn on top of the water.
- **Conclusion:** This statement is **incorrect**.

5. **Statement V: The middle zone of a candle emits the least light.**
- **Analysis:** The middle zone of a candle flame does not emit the least light; instead, the inner zone (dark zone) emits the least light. The middle zone is brighter than the inner zone.
- **Conclusion:** This statement is **incorrect**.

### Final Conclusion:
- The only correct statement is **Statement I**. Therefore, the correct answer is that **only Statement I is correct**.