Which fixative contains Formaldehyde, Distilled Water, Sodium Phosphate Monobasic, and Sodium Phosphate Dibasic and has a pH of 6.8 and is hypotonic?

• A. 10% NBF
• B. 10% Formalin Saline
• C. Formalin Alcohol
• D. Acetate Formalin

Answer: (A)

At least part of what you’re looking for is a formaldehyde solution that is buffered with phosphate salts to stay near neutral pH. The combination of Formaldehyde, Distilled Water, Sodium Phosphate Monobasic, and Sodium Phosphate Dibasic forms a phosphate-buffered formalin, which is exactly what neutral buffered formalin is. The phosphate buffer keeps the pH around 6.8–7.0, preventing the solution from becoming overly acidic, and the distilled water serves as the solvent. This buffering also helps maintain tissue morphology by keeping osmolarity relatively stable compared with non-buffered fixes.

Other fixatives listed would not match this composition: one uses a saline component (saline-based fixatives), another includes alcohol (formalin alcohol), and another uses an acetate buffer (acidic). The described mix with phosphate salts and water is characteristic of neutral buffered formalin, commonly around 10% formalin.