Correct Option
The correct option isIt does not vapourise during burning.
Explanation
A flame is defined as a region where combustion of gaseous substances takes place. The production of a flame during burning is strictly determined by the ability of the fuel to vaporize (turn into gas) upon heating.
Detailed Analysis
- Mechanism of Flame Production: Substances that vaporize during burning produce flames. For instance, in a candle, solid wax melts and turns into vapour; these vapours burn to create a flame. Similarly, kerosene oil vaporizes from the wick to burn with a flame.
- Behavior of Charcoal: Charcoal is a solid fuel that possesses a complex structure but does not vaporize significantly when heated. Since it does not release volatile gases to burn in the air above it, no flame is generated. Instead, the combustion reaction occurs directly on the surface of the solid, causing it to glow.
- Evaluation of Other Options:
- It has a very high ignition temperature. Incorrect: Ignition temperature determines the minimum temperature required to start combustion, not the nature of the combustion (flame vs. glow).
- It does not react with oxygen. Incorrect: Charcoal reacts with oxygen to release heat and carbon dioxide; if it did not react, it would not burn at all.
- It is a solid fuel. Incorrect: The solid state alone does not prevent flame formation. Solids like camphor or magnesium burn with a flame because they vaporize or produce volatile oxides during combustion.
Key Takeaway: The primary condition for a substance to burn with a flame is that it must vaporize during combustion. Substances that do not vaporize only glow.