The following are different types of sample preservation except:

• A. Freezing
• B. Reagent addition
• C. Filtration
• D. Acidification

Answer: (C)

Preservation aims to slow or halt changes in the sample by reducing temperature, adding stabilizing chemicals, or lowering pH. Freezing lowers temperature to slow biological and chemical processes. Reagent addition introduces preservatives or fixatives that inhibit growth or enzyme activity. Acidification lowers pH to deter microbes and slow reactions. Filtration, however, is a separation step used to remove solids or microorganisms from a liquid; it does not by itself prevent degradation or alter the sample's chemistry in a way that preserves it. It can be part of sample prep, but it isn’t a preservation method on its own. So filtration is the one that isn’t a preservation method.