Which of the following statements is not true?

Options

A. Flame can be seen over burning solids and liquids.
B. Type of flame depends upon the amount of oxygen available.
C. Invisible zone of a flame is the least hot zone
D. Blue zone indicates complete combustion of fuel.

Answer

To determine which of the statements is not true, we will analyze each statement provided in the question step by step.

### Step-by-Step Solution:

1. **Understanding Flame**:
- A flame is produced when a substance burns, and it can be observed in both solids and liquids.
- **Statement 1**: "Flame can be seen over burning solids and liquids."
- This statement is true because flames can indeed be observed when solids (like wood) and liquids (like oil) are burned.

2. **Types of Flame**:
- The type of flame produced during combustion depends on the amount of oxygen available.
- **Statement 2**: "The type of flame depends upon the amount of oxygen available."
- This statement is also true. Different amounts of oxygen lead to different types of combustion (complete or incomplete), which affects the flame's characteristics.

3. **Invisible Zone of Flame**:
- The flame has different zones, including the non-luminous zone (which is blue and indicates complete combustion) and the luminous zone (which is yellow and indicates incomplete combustion).
- **Statement 3**: "Invisible zone of a flame is the least hot zone."
- This statement is false. The invisible zone (non-luminous zone) is actually the hottest part of the flame due to complete combustion. Therefore, this statement is incorrect.

4. **Blue Zone and Complete Combustion**:
- The blue zone of the flame indicates complete combustion of the fuel.
- **Statement 4**: "Blue zone non-luminous zone indicates complete combustion of fuel."
- This statement is true, as the blue color signifies that there is sufficient oxygen for complete combustion.

### Conclusion:
- After analyzing all the statements, we find that **Statement 3** is not true. It incorrectly states that the invisible zone of a flame is the least hot zone, while it is actually the hottest zone.

### Final Answer:
The statement that is not true is **Statement 3**: "Invisible zone of a flame is the least hot zone."

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