Which of the following types of compounds is unable to exhibit geometrical isomerism ?

Options

A. abc = Cab
B. axC = Cay
C. aaC = Cab
D. none of these

Explanation

To determine which of the given compounds is unable to exhibit geometrical isomerism, we need to analyze the conditions required for geometrical isomerism to occur in alkenes.

### Step-by-Step Solution:

1. **Understand Geometrical Isomerism**:
Geometrical isomerism occurs in alkenes when there is restricted rotation around the double bond (C=C) and when there are different groups attached to the carbon atoms involved in the double bond. The general condition for geometrical isomerism is that:
- The two groups attached to one carbon atom of the double bond must be different (let's call them A and B).
- The two groups attached to the other carbon atom of the double bond must also be different (let's call them C and D).

2. **Analyze Each Option**:
- **Option A**: A C=C B
- Here, A and B are different. Therefore, this compound can exhibit geometrical isomerism.
- **Option B**: A X C=C A Y
- Here, A is the same on both sides of the double bond, but X and Y are different. Therefore, this compound can also exhibit geometrical isomerism.
- **Option C**: A A C=C A B
- Here, A is the same on both sides of the double bond (A and A). Therefore, this compound cannot exhibit geometrical isomerism since the condition of having different groups is not met.
- **Option D**: None of these
- This option suggests that all compounds can exhibit geometrical isomerism, which is incorrect based on our analysis.

3. **Conclusion**:
From the analysis, **Option C** (A A C=C A B) is the compound that is unable to exhibit geometrical isomerism because it does not meet the necessary conditions.

### Final Answer:
**Option C** is the correct answer as it cannot exhibit geometrical isomerism.