Which of the following species is not stable?

Options

A. `[Sn (OH)_6]^(2-)`
B. `[SiCl_6]^(2-)`
C. `[SiF_6]^(2-)`
D. `[GeCl_6]^(2-)`

Explanation

To determine which of the following species is not stable, we need to analyze the stability of each species mentioned: Sn(OH)6^2-, SiCl6^2-, SiF6^2-, and GeCl6^2-.

### Step 1: Identify the species
The species in question are:
1. Sn(OH)6^2-
2. SiCl6^2-
3. SiF6^2-
4. GeCl6^2-

### Step 2: Analyze each species for stability
1. **Sn(OH)6^2-**:
- Tin (Sn) can accommodate six hydroxide ions due to its ability to utilize d-orbitals. This species is generally stable.

2. **SiCl6^2-**:
- Silicon (Si) has a +4 oxidation state in SiCl6^2-. However, the size of the chloride ions (Cl-) is relatively large compared to the Si4+ ion. The steric hindrance and the inability of the silicon ion to accommodate six large chloride ions lead to instability. Therefore, SiCl6^2- does not exist.

3. **SiF6^2-**:
- Silicon can form stable complexes with fluoride ions (F-) because fluoride is a smaller ion compared to chloride. SiF6^2- is stable.

4. **GeCl6^2-**:
- Germanium (Ge) can also accommodate six chloride ions due to its larger size compared to silicon. GeCl6^2- is stable.

### Step 3: Conclusion
Based on the analysis, the species that is not stable is **SiCl6^2-**.

### Final Answer
The species that is not stable is **SiCl6^2-**.

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