ANS:C - The operating pressure in solvent extraction system should be below vapor pressures of all components.

In a solvent extraction system, the operating pressure should be maintained below the vapor pressures of all components involved. This is important for several reasons:

1. Prevention of Vaporization: Operating below the vapor pressures of all components ensures that none of the components vaporize during the extraction process. Vaporization of any component can lead to loss of material from the system and affect the efficiency of the extraction process.
2. Avoidance of Phase Changes: Maintaining pressure below the vapor pressures prevents phase changes, such as the formation of vapor or gas phases. Phase changes can alter the composition of the solvent and the extracted material, leading to undesirable effects on the separation process.
3. Stability of System: Operating at pressures below the vapor pressures helps maintain the stability of the system. It prevents the system from reaching conditions where vapor-liquid equilibrium occurs, ensuring that the system remains in a single-phase state throughout the extraction process.
4. Control of Process Conditions: By controlling the operating pressure below the vapor pressures of all components, operators can effectively manage the process conditions to optimize extraction efficiency and maintain product quality.

Overall, operating below the vapor pressures of all components in a solvent extraction system is essential to prevent vaporization, maintain stability, and control process conditions, ensuring efficient and effective extraction of desired components from the feed material.