Paper cup containing water does not catch fire when placed over a flame. Give reason.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Materials**: A paper cup is made of paper, which is a combustible material. However, when the paper cup is filled with water, it changes the situation.

2. **Heating the Cup**: When the paper cup is placed over a flame, heat is applied to the cup. The flame heats the bottom of the cup.

3. **Heat Transfer to Water**: The heat from the flame is conducted through the paper cup to the water inside it. This process is known as conduction, where heat moves from a hotter object (the flame) to a cooler object (the water).

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