Which of the following is commonly used as a dehydrating agent?

Alcohol is commonly used as a dehydrating agent in histopathology due to its ability to effectively remove water from tissue specimens. This dehydration process is essential for proper tissue processing, as it allows for better infiltration of embedding media, such as paraffin, which is necessary for the preparation of tissue samples for microscopic examination. Alcohol is particularly effective because it can penetrate tissues well and forms a homogeneous mixture with the embedding media, preventing the formation of artifacts.

Water, on the other hand, is a solvent and not a dehydrating agent; it would not serve the purpose of removing moisture from tissues. Formalin is primarily used as a fixative that preserves tissue morphology and structures, but it does not dehydrate tissues. Gelatin is often used in various biological applications but does not play a role in dehydration during histological processing. Therefore, alcohol stands out as the standard dehydrating agent vital for optimal tissue preparation in histopathology.