Reason for geometrical isomerism shown by 2- butene is

Options

A. Chiral carbon
B. Free rotation about single bond
C. Free rotation about double bond
D. Restricted rotation about double bond

Explanation

### Step-by-Step Solution:

1. **Understanding Geometrical Isomerism**: Geometrical isomerism (also known as cis-trans isomerism) occurs in compounds that have restricted rotation around a bond, typically a double bond. This restriction leads to different spatial arrangements of groups attached to the carbon atoms involved in the double bond.

2. **Identifying the Compound**: In this case, we are looking at 2-butene, which has the molecular formula C4H8. It consists of a double bond between the second and third carbon atoms.

3. **Drawing the Structure of 2-Butene**: The structure of 2-butene can be represented as:
- CH3-CH=CH-CH3
Here, the double bond is between the second and third carbon atoms.

4. **Analyzing the Substituents**: For geometrical isomerism to occur, each carbon involved in the double bond must have different substituents. In 2-butene:
- The second carbon (C2) has one hydrogen atom and one methyl group (CH3).
- The third carbon (C3) has one hydrogen atom and one methyl group (CH3).

5. **Identifying the Isomers**:
- **Cis-2-butene**: Both methyl groups (CH3) are on the same side of the double bond.
- **Trans-2-butene**: The methyl groups (CH3) are on opposite sides of the double bond.

6. **Conclusion**: The reason for geometrical isomerism in 2-butene is due to the restricted rotation around the double bond (C=C). This restriction prevents the free rotation that would allow the molecule to convert between different arrangements, leading to distinct isomers.

### Final Answer:
The reason for geometrical isomerism shown by 2-butene is the restricted rotation about the double bond (C=C).