Assertion Complexes containing three bidentate ligands do not show optical activity
Reason Octahedral complex `[Co(NH_(3))_(4)CI_(2)] CI` shows geometrical isomerism .

Options

A. If both `(A)` and ` (R )` are correct and `(R )` is the correct explanation of `(A ) ` .
B. If both `(A)` and ` (R )` are correct and `(R )` is the correct explanation of `(A ) ` .
C. If`(A)` is correct, but `( R )` is incorrect .
D. Both `(A)` and `(R ) ` are incorrect .

Answer

To analyze the given assertion and reason, we will break down the concepts of optical activity and geometrical isomerism in coordination compounds step by step.

### Step 1: Understanding the Assertion
The assertion states that "complexes containing three bidentate ligands do not show optical activity."

- **Bidentate Ligands**: These ligands have two donor atoms that can coordinate to a central metal atom.
- **Optical Activity**: A compound is optically active if it can exist in two non-superimposable mirror images (enantiomers). For a complex to be optically active, it must lack a plane of symmetry.

**Analysis**:
- If a complex has three bidentate ligands, it will have a total of six donor atoms coordinating to the metal. The arrangement of these ligands can lead to a symmetrical structure, which would not be optically active. However, the assertion is too general. Some arrangements of three bidentate ligands can still lead to optical isomerism depending on their spatial arrangement.

### Step 2: Understanding the Reason
The reason states that "the octahedral complex [Co(NH₃)₄Cl₂]Cl shows geometrical isomerism."

- **Geometrical Isomerism**: This type of isomerism occurs when ligands can occupy different positions around the central metal atom, leading to different spatial arrangements.
- In the case of [Co(NH₃)₄Cl₂]Cl, there can be two geometrical isomers: cis and trans.

**Analysis**:
- In the cis isomer, the two chloride ligands are adjacent to each other, while in the trans isomer, they are opposite each other. This confirms that the complex does exhibit geometrical isomerism.

### Step 3: Conclusion
Based on the analyses:
- The assertion is **incorrect** because it generalizes that three bidentate ligands cannot show optical activity, which is not universally true.
- The reason is **correct** because the complex [Co(NH₃)₄Cl₂]Cl does show geometrical isomerism.

### Final Answer
- Assertion: Incorrect
- Reason: Correct