Which of the following cannot show linkage isomerism?

Options

A. `NO_(2)^(-)`
B. `NH_(3)`
C. `CN^(-)`
D. `SCN^(-)`

Answer

To determine which ligand cannot show linkage isomerism, we need to analyze the nature of the ligands provided in the options. Linkage isomerism occurs when a ligand can coordinate to a metal ion through different atoms. This typically requires the ligand to be ambidentate, meaning it has more than one potential donor atom.

### Step-by-Step Solution:

1. **Understand Linkage Isomerism**:
- Linkage isomerism occurs when a ligand can bind to a metal ion through different atoms. For a ligand to exhibit this property, it must have multiple donor atoms.

2. **Identify Ambidentate Ligands**:
- Ambidentate ligands are those that have more than one atom capable of donating a pair of electrons to the metal ion. Examples include:
- **NO2**: Can bind through nitrogen (N) or oxygen (O).
- **Cyanide (CN)**: Can bind through carbon (C) or nitrogen (N).
- **Thiocyanate (SCN)**: Can bind through sulfur (S) or nitrogen (N).

3. **Analyze the Ligands**:
- **NO2**: Ambidentate (can bind through N or O).
- **Cyanide (CN)**: Ambidentate (can bind through C or N).
- **Thiocyanate (SCN)**: Ambidentate (can bind through S or N).
- **Ammonia (NH3)**: Not ambidentate (only has one donor atom, nitrogen).

4. **Conclusion**:
- Among the ligands mentioned, ammonia (NH3) cannot show linkage isomerism because it has only one donor atom (nitrogen) and does not have multiple binding sites.

### Final Answer:
The ligand that cannot show linkage isomerism is **NH3** (option 2).

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