Which fixative contains acetic acid?

• A. Zenker
• B. Bouin
• C. Carnoy
• D. Formol-saline

Answer: (A)

Acetic acid is added to certain fixatives to help preserve nucleic acids and improve nuclear detail by slightly swelling and coagulating cellular proteins, aiding penetration of the fixative. Zenker's fixative includes acetic acid along with mercuric chloride and potassium dichromate, and the acetic acid component contributes to better nuclear preservation and contrast in staining. That combination is characteristic of Zenker and explains why it’s the fixative containing acetic acid among the options. (Note: other fixatives on the list, such as Bouin's and Carnoy's, also contain acetic acid, while Formol-saline does not.)