An alkene exists as geometrical isomers. The minimum number of carbon atoms in the molecule is

Options

A. 2
B. 3
C. 4
D. 6

Explanation

To determine the minimum number of carbon atoms in an alkene that can exhibit geometrical isomerism, we need to analyze the structure of alkenes and the conditions required for geometrical isomerism to occur.

### Step-by-Step Solution:

1. **Understanding Geometrical Isomerism**:
- Geometrical isomerism occurs in alkenes when there is restricted rotation around the double bond and when the substituents attached to the double-bonded carbon atoms are different.

2. **Identifying the Smallest Alkene**:
- The simplest alkene is ethene (C2H4), which has the structure H2C=CH2. Since both carbon atoms have identical substituents (hydrogens), ethene cannot exhibit geometrical isomerism.

3. **Examining Propene**:
- The next alkene is propene (C3H6), with the structure CH2=CH-CH3. Here, the first carbon has two hydrogens and the second carbon has one hydrogen and one methyl group (CH3). Since the first carbon has identical substituents, propene also does not show geometrical isomerism.

4. **Considering Butene**:
- The smallest alkene that can exhibit geometrical isomerism is butene (C4H8). There are two isomers of butene: 1-butene (CH2=CH-CH2-CH3) and 2-butene (CH3-CH=CH-CH3).
- In 2-butene, the second carbon has one hydrogen and one methyl group (CH3), while the third carbon has one hydrogen and one methyl group (CH3). This allows for two different configurations:
- **Cis-2-butene**: Both methyl groups are on the same side of the double bond.
- **Trans-2-butene**: The methyl groups are on opposite sides of the double bond.

5. **Conclusion**:
- Since 2-butene is the first alkene that can show geometrical isomerism and it contains 4 carbon atoms, the minimum number of carbon atoms in an alkene that can exhibit geometrical isomerism is **4**.

### Final Answer:
The minimum number of carbon atoms in the molecule is **4**.