**Core Concept**
The fixation of cervical smear involves the use of a preservative solution to preserve the cellular morphology and prevent degradation of the cells. This is crucial for accurate cytological diagnosis of cervical lesions.

**Why the Correct Answer is Right**
The correct answer is Ethyl alcohol (95%). Ethyl alcohol is used as a fixative in cervical smear preparation because it rapidly kills the cells, thereby preventing further metabolic activity and preserving the cellular morphology. This is essential for accurate cytological diagnosis.

* Ethyl alcohol denatures proteins, making it difficult for microorganisms to grow and multiply, thereby preventing contamination.
* The use of ethyl alcohol as a fixative also helps to preserve the cellular architecture, which is critical for the diagnosis of cervical lesions.

**Why Each Wrong Option is Incorrect**
**Option A:** Acetic acid is used as a fixative in cervical smear preparation, but it is not the most commonly used fixative. Acetic acid is used to enhance the visibility of cellular details and to prevent bleeding from the vaginal epithelium.

**Option B:** Formalin is a fixative used in histopathology, but it is not used for cervical smear preparation. Formalin is a strong fixative that preserves the cellular morphology, but it is not suitable for cytological diagnosis.

**Option C:** Glutaraldehyde is a fixative used in electron microscopy, but it is not used for cervical smear preparation. Glutaraldehyde is a strong fixative that preserves the ultrastructural details of cells, but it is not suitable for light microscopy.

**Clinical Pearl / High-Yield Fact**
It is essential to use a fixative that is suitable for cytological diagnosis, as incorrect fixation can lead to false-negative or false-positive results. Always follow standard protocols for cervical smear preparation to ensure accurate diagnosis.

**Correct Answer:** C. Ethyl alcohol (95%).