Which of the following statements are true ?
I. Yellow flames are ideal for heating.
II. The substances which vaporise during burning give flames.
III. Luminous zone contains unburnt carbon particles.
IV. The non-luminous zone has the highest temperature.

Options

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

Explanation

To determine which of the statements are true, let's analyze each statement one by one:

### Step 1: Analyze Statement I
**Statement I:** Yellow flames are ideal for heating.
- **Explanation:** Yellow flames indicate incomplete combustion, which means that there is not enough oxygen for the fuel to burn completely. This results in the production of soot (unburnt carbon particles) and lower heat output. Therefore, yellow flames are not ideal for heating.
- **Conclusion:** This statement is **false**.

### Step 2: Analyze Statement II
**Statement II:** The substances which vaporize during burning give flames.
- **Explanation:** For a flame to be produced, the fuel must vaporize. When the vaporized fuel combines with oxygen and ignites, it produces a flame. Thus, this statement is true.
- **Conclusion:** This statement is **true**.

### Step 3: Analyze Statement III
**Statement III:** Luminous zone contains unburnt carbon particles.
- **Explanation:** The luminous zone of a flame is bright yellow due to the presence of unburnt carbon particles. Incomplete combustion occurs here, leading to the accumulation of these particles. Therefore, this statement is true.
- **Conclusion:** This statement is **true**.

### Step 4: Analyze Statement IV
**Statement IV:** The non-luminous zone has the highest temperature.
- **Explanation:** The non-luminous zone is the outer part of the flame where complete combustion occurs, resulting in the highest temperature. This zone does not produce light but generates the most heat. Therefore, this statement is true.
- **Conclusion:** This statement is **true**.

### Final Conclusion
Based on the analysis:
- Statement I is **false**.
- Statements II, III, and IV are **true**.

Thus, the correct answer is that statements II, III, and IV are true.

### Summary of True Statements:
- II. The substances which vaporize during burning give flames. (True)
- III. Luminous zone contains unburnt carbon particles. (True)
- IV. The non-luminous zone has the highest temperature. (True)