Which of the following species does not exist ?

Options

A. `PbCl_(2)`
B. `BiCl_(5)`
C. `PbI_(4)`
D. `BiI_(3)`

Answer

To determine which species does not exist among the given compounds, we will analyze each compound based on their oxidation states and the inert pair effect.

### Step-by-Step Solution:

1. **Identify the Compounds**:
Let's assume the compounds in question are A (BCl5), B (PbI4), C (another compound), and D (a stable compound).

2. **Analyze BCl5**:
- Bismuth (Bi) is in the +5 oxidation state in BCl5.
- Bismuth belongs to Group 15, where elements can exhibit +3 and +5 oxidation states.
- However, due to the **inert pair effect**, the +5 oxidation state is unstable for heavier elements like bismuth.
- The inert pair effect refers to the reluctance of the s-electrons to participate in bonding, making +3 the more stable oxidation state.
- Therefore, BCl5 does not exist.

3. **Analyze PbI4**:
- Lead (Pb) is in the +4 oxidation state in PbI4.
- Lead belongs to Group 14, where it can exhibit +2 and +4 oxidation states.
- Similar to bismuth, the +4 oxidation state is unstable for lead due to the inert pair effect.
- The +2 oxidation state is more stable, leading to the conclusion that PbI4 cannot exist.
- Instead, PbI2 is stable and exists.

4. **Conclusion**:
- Both BCl5 and PbI4 do not exist due to the instability of their higher oxidation states caused by the inert pair effect.
- Therefore, the answer to the question is that B (BCl5) and C (PbI4) do not exist.

### Final Answer:
The species that does not exist are BCl5 and PbI4.