The phenomenon involving the migration of a proton to give two structural isomers in equilibrium with each other is known is –

Options

A. Matamerism
B. Tautomerism
C. Cis trans isomerism
D. Stereo isomerism

Answer

To solve the question regarding the phenomenon involving the migration of a proton to give two structural isomers in equilibrium with each other, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about a phenomenon where a proton migrates, resulting in two structural isomers that are in equilibrium. This indicates a specific type of isomerism.

2. **Identifying the Options**: The options provided are:
- Metamers
- Tautomerism
- Cis-Trans Isomerism
- Stereoisomerism

3. **Analyzing Each Option**:
- **Metamers**: This type of isomerism arises due to different alkyl groups on either side of a functional group. It involves the shifting of entire alkyl groups, not protons. Therefore, this option is not correct.

- **Tautomerism**: This is the phenomenon where a proton migrates (specifically a hydrogen atom) between two different positions in a molecule, leading to structural isomers that are in equilibrium. A common example is the keto-enol tautomerism, where a ketone can convert to its corresponding enol form through the migration of a hydrogen atom. This matches the description given in the question.

- **Cis-Trans Isomerism**: Also known as geometric isomerism, this involves the arrangement of groups around a double bond or a ring structure. It does not involve the migration of protons, so this option is also incorrect.

- **Stereoisomerism**: This is a broader category that includes both geometric and optical isomers. While it involves different spatial arrangements of atoms, it does not specifically refer to the migration of protons. Thus, this option is not applicable.

4. **Conclusion**: Based on the analysis, the correct answer is **Tautomerism**, as it specifically involves the migration of a proton leading to two structural isomers in equilibrium.

### Final Answer:
The phenomenon involving the migration of a proton to give two structural isomers in equilibrium with each other is known as **Tautomerism**.