ANS:D - both (b) and (c)

1. For Heat-Sensitive Materials: Many compounds can degrade or undergo unwanted chemical reactions when exposed to high temperatures. Heat-sensitive materials are substances that are particularly susceptible to these effects. In conventional distillation processes, high temperatures are often necessary to achieve separation, which can lead to the degradation of these materials. Molecular distillation, however, operates at lower temperatures compared to traditional distillation techniques. By reducing the pressure in the distillation apparatus, the boiling point of the materials can be lowered, allowing separation to occur at lower temperatures. This minimizes the risk of thermal degradation or other undesirable chemical reactions, making molecular distillation a preferred method for handling heat-sensitive substances.
2. Very Low Pressure Distillation: In addition to being suitable for heat-sensitive materials, molecular distillation operates under very low pressures. By reducing the pressure within the distillation apparatus to levels significantly below atmospheric pressure, the boiling point of the substances being distilled is further decreased. This is advantageous for several reasons:
   • Lowering the boiling point allows for separation to occur at lower temperatures, which is beneficial for heat-sensitive materials.
   • It reduces the risk of thermal decomposition or other chemical reactions that may occur at higher temperatures.
   • It enables the separation of compounds with very close boiling points, which might not be feasible using traditional distillation methods at atmospheric pressure.
   • It can enhance the efficiency and purity of the distillation process by minimizing the formation of unwanted by-products or impurities.

In summary, molecular distillation combines the advantages of operating at very low pressures with the ability to handle heat-sensitive materials, making it a valuable technique in various industries such as pharmaceuticals, food processing, and chemical engineering.