Which out of the following compound does not exist?

Options

A. `BF_(3)`
B. `TlCl_(3)`
C. `TlCl_(5)`
D. Both (B) and (C)

Explanation

To determine which compound does not exist among the given options, we need to analyze the oxidation states of the elements involved in the compounds.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- We need to look at the compounds provided in the question. Let's assume the options are:
- A) BF3
- B) AlCl3
- C) TlCl5
- D) GaCl3

2. **Check the Existence of Each Compound**:
- **BF3 (Boron Trifluoride)**:
- Boron can have an oxidation state of +3 in BF3. This compound is well-known and exists.
- **AlCl3 (Aluminum Chloride)**:
- Aluminum can have an oxidation state of +3 in AlCl3. This compound also exists.
- **GaCl3 (Gallium Trichloride)**:
- Gallium can have an oxidation state of +3 in GaCl3. This compound exists as well.
- **TlCl5 (Thallium Pentachloride)**:
- Thallium typically has oxidation states of +1 and +3. It cannot exhibit an oxidation state of +5 due to its electronic configuration and stability. Therefore, TlCl5 does not exist.

3. **Conclusion**:
- From the analysis, we find that the compound **TlCl5** does not exist due to the inability of thallium to exhibit a +5 oxidation state.

### Final Answer:
- The compound that does not exist is **option C: TlCl5**.