Formaldehyde solutions used for fixation are concentrated at 37-40% by weight.

• A. True
• B. False
• C. Not enough information
• D. Not applicable

Answer: (A)

The main idea is that the fixative you start with is a concentrated formaldehyde solution. The standard stock form, formalin, is about 37% formaldehyde by weight (often cited as 37–40%). This concentrated solution is what laboratories use to prepare the actual fixative solutions applied to tissue, which are typically diluted down to around 3.7–4% formaldehyde for fixation (for example, 10% neutral buffered formalin). So, saying that formaldehyde solutions used for fixation are concentrated at 37–40% by weight is accurate for the stock material from which fixatives are made.