which alkene will not show geometrical isomerism ?

Options

A. `XYC = CXY`
B. `XYC = CXZ`
C. `XYC = CZW`
D. `XYC = CXX`

Answer

To determine which alkene will not show geometrical isomerism, we need to understand the conditions required for geometrical (cis-trans) isomerism to occur in alkenes.

### Step-by-Step Solution:

1. **Identify the Structure of Alkenes**: Geometrical isomerism occurs in alkenes when there are two different groups attached to each carbon of the double bond. This means that the double bond must have two different substituents on each carbon atom involved in the double bond.

2. **Analyze Each Option**:
- **Option 1: 5-methyl-oct-6-ene-3-yne**: This compound has a double bond at the 6th position. We need to check the substituents on the carbons involved in the double bond.
- **Option 2: 5-methyl-oct-3-yne-6-ene**: This compound has a double bond at the 6th position as well. We will analyze the substituents similarly.
- **Option 3: 4-methyl-oct-5-yne-2-ene**: This compound has a double bond at the 2nd position. We will check the substituents.
- **Option 4: 4-methyl-oct-2-ene-5-yne**: This compound has a double bond at the 2nd position. We will check the substituents here as well.

3. **Check for Geometrical Isomerism**:
- For **Option 1**: The double bond at the 6th position has different groups on both carbons, so it can show geometrical isomerism.
- For **Option 2**: The double bond at the 6th position also has different groups, so it can show geometrical isomerism.
- For **Option 3**: The double bond at the 2nd position has different groups on both carbons, so it can show geometrical isomerism.
- For **Option 4**: The double bond at the 2nd position has identical groups on one of the carbons (the methyl group is the same), which means it cannot show geometrical isomerism.

4. **Conclusion**: After analyzing all options, **Option 4 (4-methyl-oct-2-ene-5-yne)** is the alkene that will not show geometrical isomerism due to the presence of identical substituents on one of the carbons of the double bond.

### Final Answer:
**Option 4: 4-methyl-oct-2-ene-5-yne will not show geometrical isomerism.**