The clouds consist of charged particles of water dispersed in air.Some of them are +vely charged, others are -vely charged.When +vely charged clouds come closer they cause lightening and thundering whereas when +ve and -ve charged colloids come closer they cause heavy rain by aggregration of minute particles.It is possible to cause artifical rain by throwing electrified sand or silver iodide from an aeroplane and thus coagulating the mist hangind in air.
Smoke screens consist of

Options

A. fine particles of `TiO_2` dispersed in air by aeroplanes
B. fine particles of Agl dispersed in air by aeroplanes
C. fine partilces of `Al_2O_3` dispersed in air by aeroplanes
D. None of these

Explanation

### Step-by-Step Solution:

1. **Understanding the Concept of Smoke Screens**:
- Smoke screens are used to obscure vision and can be created using fine particles that are dispersed in the air.

2. **Identifying the Material Used**:
- The question hints at the use of fine particles to create a smoke screen. Common materials used for this purpose include various compounds that can effectively scatter light.

3. **Determining the Correct Compound**:
- In the video transcript, it is mentioned that fine particles of titanium dioxide (TiO2) are used to create smoke screens. TiO2 is known for its high refractive index and ability to scatter light, making it suitable for this application.

4. **Conclusion**:
- Therefore, the smoke screen consists of fine particles of titanium dioxide (TiO2).

### Final Answer:
- Smoke screens consist of fine particles of **TiO2**.

---