The correct option is (a).
Explanation
A flame is the visible, gaseous part of a fire. It is produced only when substances vaporize during burning. If a substance does not vaporize, it does not produce a flame and instead burns with a glow.
Statement-wise Analysis:
- 1. Magnesium (Correct): Magnesium is a metal that vaporizes upon heating and burns with a dazzling white flame to form magnesium oxide.
- 2. Camphor (Correct): Camphor is a volatile substance. When heated, it sublimates (turns directly from solid to gas) and burns with a distinct flame.
- 3. Charcoal (Incorrect): Charcoal is a carbon-rich solid that does not vaporize significantly. It burns by glowing red (incandescence) without producing a flame.
- 4. Coal (Incorrect): While coal contains some volatile matter, in the context of flame formation classification, it is primarily categorized with charcoal as a substance that glows rather than producing a sustained flame like wax or camphor.
Key Takeaway:
Only substances that vaporize during combustion produce a flame; substances that remain solid while burning only glow.