How many of the following compounds are found to exist?
`BiF_(5), PbO_(2), SnCI_(2), Tl_(2)O_(3), PbI_(4), As_(2)O_(3)`

Explanation

To determine how many of the given compounds exist, we will analyze each compound one by one based on known chemical stability and oxidation states.

1. **BiF₅ (Bismuth Pentafluoride)**:
- Bismuth typically exhibits oxidation states of +3 and +5. However, BiF₅ is known to be unstable and does not exist under normal conditions.
- **Conclusion**: Does not exist.

2. **PbO₂ (Lead(IV) Oxide)**:
- Lead can exist in +2 and +4 oxidation states. PbO₂ is stable and is a known compound.
- **Conclusion**: Exists.

3. **SnCl₂ (Tin(II) Chloride)**:
- Tin can exist in +2 and +4 oxidation states. SnCl₂ is a stable compound and is commonly found.
- **Conclusion**: Exists.

4. **Tl₂O₃ (Thallium(III) Oxide)**:
- Thallium can exist in +1 and +3 oxidation states. Tl₂O₃ is a known and stable compound.
- **Conclusion**: Exists.

5. **PbI₄ (Lead(IV) Iodide)**:
- Similar to PbO₂, lead can also exhibit +4 oxidation state with iodine. However, PbI₄ is unstable because lead(IV) is easily reduced to lead(II) and iodine is oxidized to I₂. Therefore, PbI₄ does not exist.
- **Conclusion**: Does not exist.

6. **As₂O₃ (Arsenic(III) Oxide)**:
- Arsenic can exist in +3 and +5 oxidation states. As₂O₃ is a stable compound and is well-documented.
- **Conclusion**: Exists.

Now, summarizing the existence of the compounds:
- **Exist**: PbO₂, SnCl₂, Tl₂O₃, As₂O₃ (4 compounds)
- **Do not exist**: BiF₅, PbI₄ (2 compounds)

**Final Answer**: Out of the six compounds listed, **four** are found to exist.