Which of the following molecules`(s)is//are` not showing optical isomerism ? .

Options

A. `a.[Co(NH_(3))_(3)Cl]^(o+)`
B. `b.[Cr(H_(2)O)_(6)]^(3+)`
C. `c.[Zn(NH_(3))_(6)]^(2+)`
D. `d.[Sc(H_(2)O)_(3)(NH_(3))_(3)]^(3+)`

Answer

To determine which of the given molecules do not show optical isomerism, we need to analyze the molecular structures based on their coordination number and geometry. Here's a step-by-step solution:

### Step 1: Understand Optical Isomerism
Optical isomerism occurs when a molecule can exist in two forms that are mirror images of each other (enantiomers). For a molecule to exhibit optical isomerism, it must lack an internal plane of symmetry.

### Step 2: Analyze Each Compound
1. **Compound MA3B**:
- This compound has a coordination number of 4 and can adopt a tetrahedral or square planar geometry.
- In tetrahedral complexes, if all three A ligands and one B ligand are different, it can show optical isomerism. However, if A is identical, it can lead to a plane of symmetry.
- Therefore, MA3B can potentially show optical isomerism depending on the ligands.

2. **Compound MA6**:
- This compound has a coordination number of 6 and typically adopts an octahedral geometry.
- In octahedral complexes, if all six ligands are the same, there is no possibility of optical isomerism as it has a plane of symmetry.
- Therefore, MA6 does not show optical isomerism.

3. **Compound MA6 (again)**:
- This is a repeat of the previous analysis and will yield the same conclusion. MA6 does not show optical isomerism.

4. **Compound MA3B3**:
- This compound has a coordination number of 6 and can also adopt an octahedral geometry.
- If A and B are different, it can form optical isomers as it can exist in two non-superimposable mirror images.
- Therefore, MA3B3 can show optical isomerism.

### Step 3: Conclusion
Based on the analysis:
- **MA3B**: May show optical isomerism depending on the ligands.
- **MA6**: Does not show optical isomerism.
- **MA6 (again)**: Does not show optical isomerism.
- **MA3B3**: Shows optical isomerism.

Thus, the compounds that do not show optical isomerism are **MA6** and the repeated **MA6**.

### Final Answer
The molecules that do not show optical isomerism are **MA6** and **MA6**.

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