Which statement about serial dilutions is NOT true?

• A. The final volume is not necessarily equal to the initial stock volume.
• B. The steps must be performed accurately.
• C. The final concentration is the same as the stock.
• D. The dilution factor is applied at each step.

Answer: (C)

Serial dilutions reduce the concentration step by step using a fixed dilution factor. Each step takes a measured amount from the previous tube and adds diluent to reach a new, larger total volume, so the concentration drops by that factor with every transfer. After n steps, the concentration becomes the stock concentration divided by the dilution factor raised to the n-th power (C_final = C_stock / DF^n). That means the final concentration is not the same as the stock.

This is why the statement about the final concentration being the same as the stock isn’t true. The other points hold: the final volume is not necessarily equal to the initial stock volume because diluent is added to reach each next step; the steps must be performed accurately to obtain the intended concentrations; and the dilution factor is applied at each step to achieve the overall dilution.