Which of the following halides is least stable and has doubtful existence ?

Options

A. `C Cl_4`
B. `Snl_4`
C. `Gel_4`
D. `Pbl_4`

Explanation

To determine which of the given halides is least stable and has doubtful existence, we will analyze each option based on the stability of their oxidation states and the inert pair effect.

### Step-by-Step Solution:

1. **Identify the Compounds**: The options provided are CCl4, SnCl4, GeCl4, and PbCl4.

2. **Analyze CCl4**:
- CCl4 (Carbon Tetrachloride) is a covalent compound where carbon has a complete octet.
- Since carbon is in a stable +4 oxidation state, CCl4 is stable and exists in nature.

3. **Examine the Other Halides (SnCl4, GeCl4, PbCl4)**:
- These compounds involve elements from Group 14 (Carbon Group) and are in the +4 oxidation state.
- As we move down the group from Ge to Sn to Pb, the stability of the +4 oxidation state decreases due to the inert pair effect.

4. **Understanding the Inert Pair Effect**:
- The inert pair effect refers to the tendency of the s-electrons to remain non-bonding in heavier elements.
- For Sn, Ge, and Pb, the +4 oxidation state becomes less stable as we go down the group:
- Ge (Germanium) +4 is more stable than Sn (Tin) +4.
- Sn +4 is more stable than Pb (Lead) +4.

5. **Conclusion on Stability**:
- Among SnCl4, GeCl4, and PbCl4, PbCl4 is the least stable due to the inert pair effect, which makes the +4 oxidation state of lead less favorable.
- Therefore, PbCl4 has a doubtful existence compared to the other halides.

6. **Final Answer**:
- The halide that is least stable and has doubtful existence is **PbCl4**.