Number of materials which on burning form a flame is __________ .
Wax, camphor, LPG, magnesium ribbon, candle, kerosene oil, charcoal

Explanation

To determine the number of materials that produce a flame when burned from the given list: Wax, camphor, LPG, magnesium ribbon, candle, kerosene oil, and charcoal, we will analyze each material based on whether it vaporizes during burning, as only those that vaporize can produce a flame.

### Step-by-Step Solution:

1. **Identify the materials**: The materials given are:
- Wax
- Camphor
- LPG (Liquefied Petroleum Gas)
- Magnesium ribbon
- Candle
- Kerosene oil
- Charcoal

2. **Analyze each material**:
- **Wax**: When burned, wax vaporizes and produces a flame. (Produces flame)
- **Camphor**: Camphor also vaporizes when burned and produces a flame. (Produces flame)
- **LPG**: LPG is a gas that vaporizes easily and produces a flame when burned. (Produces flame)
- **Magnesium ribbon**: When magnesium ribbon burns, it produces a bright flame, but it does not vaporize in the same way as the others. However, it still produces a flame. (Produces flame)
- **Candle**: A candle is made of wax, which vaporizes when burned, producing a flame. (Produces flame)
- **Kerosene oil**: Kerosene oil vaporizes when burned and produces a flame. (Produces flame)
- **Charcoal**: Charcoal does not vaporize in the same way as the others; it burns but does not produce a flame. (Does not produce flame)

3. **Count the materials that produce a flame**:
- The materials that produce a flame are: Wax, Camphor, LPG, Magnesium ribbon, Candle, and Kerosene oil.
- Total materials producing flame = 6

### Final Answer:
The number of materials which on burning form a flame is **6**.

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