ANS:C - freeze

Heat-sensitive materials like certain pharmaceuticals and foodstuffs can be dried in a freeze dryer. Freeze drying, also known as lyophilization, is a dehydration process used to preserve perishable materials or make them more convenient for transport. It involves freezing the material and then reducing the surrounding pressure to allow the frozen water (ice) in the material to sublime directly from the solid phase to the gas phase, bypassing the liquid phase. This process preserves the structure and integrity of the heat-sensitive materials, as they are dried under low temperatures. Therefore, freeze drying is well-suited for drying heat-sensitive materials such as pharmaceuticals and foodstuffs without subjecting them to high temperatures that could degrade their quality or efficacy. Freezing is a process in which a liquid substance is converted into a solid state by lowering its temperature below its freezing point. During freezing, the molecules in the liquid slow down and eventually form an ordered, crystalline structure characteristic of the solid phase. Here's a brief overview of the freezing process:

1. Lowering Temperature: The temperature of the substance is gradually lowered below its freezing point. As the temperature decreases, the thermal energy of the molecules decreases, causing them to move more slowly.
2. Formation of Crystals: As the temperature continues to decrease, the molecules start to arrange themselves into a crystalline structure. This process is driven by the attractive forces between the molecules, which cause them to align in a regular pattern.
3. Solidification: Once a sufficient number of molecules have arranged themselves into a crystalline structure, the substance solidifies and becomes a solid. At this point, the substance has reached its freezing point, and further cooling will not result in any additional phase changes.

Freezing is commonly used for food preservation, as it can inhibit the growth of microorganisms and slow down chemical reactions that cause spoilage. It is also used in various industrial processes, such as the production of ice, the preservation of biological samples, and the manufacturing of certain products.