In tautomerism, the two tautomeric forms continuously change into each other through the oscillation of

Options

A. a proton
B. `pi`-electrons
C. a proton and `pi`-electrons
D. none of the above.

Explanation

To solve the question regarding tautomerism and the oscillation of species involved, we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Understanding Tautomerism**:
Tautomerism is a special type of isomerism where two isomers (tautomers) exist in dynamic equilibrium and differ in the position of a proton and the arrangement of electrons.

2. **Identifying Tautomeric Forms**:
A common example of tautomerism is the equilibrium between ketones and enols. For instance, propanone (CH3C(=O)CH3) can tautomerize to its enol form (CH3C(OH)=CH2).

3. **Proton Transfer**:
In the tautomerization process, a proton (H+) is transferred from the alpha carbon (the carbon adjacent to the carbonyl group) to the oxygen atom in the carbonyl group. This transfer is crucial in converting the ketone to the enol form.

4. **Electron Movement**:
Along with the proton transfer, there is also a movement of electrons. Specifically, the pi electrons from the carbonyl double bond shift to form a new bond with the oxygen atom, while the electrons from the C-H bond are involved in the formation of the new double bond in the enol.

5. **Conclusion**:
Therefore, the two tautomeric forms continuously change into each other through the oscillation of both a proton and pi electrons.

### Final Answer:
The correct answer is **C: a proton and pi electrons**.