10% formalin is a 1:4 dilution of commercial formalin.

• A. True
• B. False
• C. It is a 1:9 dilution
• D. It is undiluted

Answer: (B)

The idea being tested is how a concentrated formalin solution is diluted to a standard 10% formalin. Commercial formalin is a concentrated formaldehyde solution, and “10% formalin” refers to a solution where the active formaldehyde content is about ten percent by volume. Diluting the concentrated stock to that level is not done by a simple 1 to 4 ratio. A 1:4 dilution would produce a final solution with a formaldehyde concentration lower than ten percent. Therefore the statement is not correct. In practice, reaching ten percent requires a dilution ratio different from 1:4.