Number of materials out of the following, which are poor conductor of electricity is ___________ .
Wood, distilled water, iron nail, aluminium foil, eraser,silver ring, coal piece, comb, coin, tapwater

Explanation

To determine the number of materials that are poor conductors of electricity from the given list, we need to analyze each material based on its conductivity properties.

1. **Wood**: Wood is known to be a poor conductor of electricity. It does not allow electricity to pass through it.
- **Hint**: Think about materials that are natural and non-metallic.

2. **Distilled Water**: Distilled water is pure and does not contain any dissolved ions or minerals, making it a poor conductor of electricity.
- **Hint**: Consider the purity of water and its effect on conductivity.

3. **Iron Nail**: Iron is a metal and has free electrons that allow it to conduct electricity well. Therefore, it is not a poor conductor.
- **Hint**: Metals generally conduct electricity due to the presence of free-moving electrons.

4. **Aluminium Foil**: Aluminium is also a metal and is a good conductor of electricity. Thus, it is not a poor conductor.
- **Hint**: Similar to iron, think about the properties of metals.

5. **Eraser**: An eraser is typically made of rubber or similar materials, which are poor conductors of electricity.
- **Hint**: Consider common stationery items and their electrical properties.

6. **Coal Piece**: Coal is a form of carbon and is generally a poor conductor of electricity.
- **Hint**: Reflect on non-metallic materials and their conductivity.

7. **Comb**: A plastic comb is a poor conductor of electricity. Plastics are generally insulators.
- **Hint**: Think about materials that are used for insulation.

8. **Coin**: Coins are usually made of metals, which are good conductors of electricity. Therefore, they are not poor conductors.
- **Hint**: Again, consider the properties of metals.

9. **Tap Water**: Tap water usually contains various dissolved ions, making it a good conductor of electricity.
- **Hint**: Think about the impurities in water and how they affect conductivity.

Now, let's summarize the materials that are poor conductors of electricity:

- Wood: Poor conductor
- Distilled Water: Poor conductor
- Iron Nail: Good conductor
- Aluminium Foil: Good conductor
- Eraser: Poor conductor
- Coal Piece: Poor conductor
- Comb: Poor conductor
- Coin: Good conductor
- Tap Water: Good conductor

Counting the poor conductors, we have:
1. Wood
2. Distilled Water
3. Eraser
4. Coal Piece
5. Comb

Thus, the total number of materials that are poor conductors of electricity is **5**.

**Final Answer**: 5