Which of the following isomerism is not shown by alkenes.

Options

A. Geometrical isomerism
B. Optical isomerism
C. Metamerism
D. Ring chain isomerism

Explanation

To determine which type of isomerism is not shown by alkenes, we will analyze the four types of isomerism mentioned: position isomerism, chain isomerism, geometrical isomerism, and metamerism.

### Step-by-Step Solution:

1. **Identify the Types of Isomerism**:
- The types of isomerism we need to consider are:
- Position isomerism
- Chain isomerism
- Geometrical isomerism
- Metamerism

2. **Position Isomerism**:
- Position isomerism occurs when the position of the double bond in the carbon chain changes while keeping the same molecular formula.
- Example: But-1-ene (CH3CH2CH=CH2) and But-2-ene (CH3CH=CHCH3) are position isomers.
- **Conclusion**: Alkenes can exhibit position isomerism.

3. **Chain Isomerism**:
- Chain isomerism arises from different arrangements of the carbon skeleton.
- Example: Butene (C4H8) can exist as but-1-ene and 2-methylpropene.
- **Conclusion**: Alkenes can exhibit chain isomerism.

4. **Geometrical Isomerism**:
- Geometrical isomerism (cis-trans isomerism) occurs due to restricted rotation around the double bond.
- Example: But-2-ene can exist as cis-but-2-ene and trans-but-2-ene.
- **Conclusion**: Alkenes can exhibit geometrical isomerism.

5. **Metamerism**:
- Metamerism occurs due to the different alkyl groups around a polyvalent functional group or atom.
- This type of isomerism is typically associated with ethers and ketones, not alkenes.
- **Conclusion**: Alkenes do not exhibit metamerism.

6. **Final Answer**:
- The type of isomerism that is not shown by alkenes is **metamerism**.